Ultrasonic actuator with power supply electrode arrangement

ABSTRACT

An ultrasonic actuator may be provided in which generation of a stress is prevented in the connection face of the piezoelectric element between the electrodes and the conductive members. The ultrasonic actuator includes a piezoelectric element (P 1 ) and flexible cables (F 1 ). The piezoelectric element (P 1 ) includes: a piezoelectric layer ( 1 ); a power supply electrode ( 2 ) provided on a principal surface of the piezoelectric layer ( 1 ); a counter electrode ( 3 ) provided to face the power supply electrode ( 2 ) with the piezoelectric layer ( 1 ) interposed therebetween; a power supply external electrode ( 4 ) which is provided on a short-side surface of the piezoelectric element (P 1 ), and is electrically coupled to the power supply electrode ( 2 ); and a counter external electrode ( 5 ) which is provided on a short-side surface of the piezoelectric element (P 1 ), and is electrically coupled to the counter electrode ( 3 ). The flexible cables (F 1 ) include a first flexible cable (F 11 ) connected to the power supply external electrode ( 4 ), and a second flexible cable (F 12 ) connected to the counter external electrode ( 5 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT International PatentApplication No. PCT/JP2008/003629 filed on Dec. 5, 2008, which claimspriority of Japanese Patent Application No. 2007-315630 filed on Dec. 6,2007, the entire contents of which are expressly incorporated byreference herein.

BACKGROUND

The present invention relates to an ultrasonic actuator which includes apiezoelectric element.

Conventionally, an ultrasonic actuator is known which includes apiezoelectric element (electromechanical conversion element) for use invarious electric devices and other types of devices (e.g., see PatentDocument 1). This piezoelectric element is formed by alternatelystacking piezoelectric bodies and electrodes. In the ultrasonicactuator, voltages are applied to the electrodes to cause thepiezoelectric element to vibrate, whereby a movable element is moved.

Another ultrasonic actuator is known in which the piezoelectric elementis energized to generate the first vertical vibration in a drivingdirection and the second bending direction in a direction perpendicularto the driving direction so that a vibrator provided in thepiezoelectric element make an orbital movement which is a synthesis ofthe vertical vibration and the bending vibration, whereby a movableelement is moved (e.g., see Patent Document 2).

To apply voltages to the electrodes of the piezoelectric element, theelectrodes are connected to conductive members.

Patent Document 1: Japanese Laid-Open PCT National-Phase Publication No.2003-501988

Patent Document 2: Japanese Laid-Open Patent Publication No. 2000-295876

SUMMARY

In the piezoelectric element described in Patent Document 1, theelectrodes and the conductive members are connected in a plane which isperpendicular to a surface of a piezoelectric body provided with theelectrodes and which is parallel to the long sides of the surface of thepiezoelectric body provided with the electrodes. Vibration of thepiezoelectric element deforms the connection face and generates a stresstherein. As a result, the connected portion between the electrodes andthe conductive members is subjected to a stress, and there is aprobability that peeling of the connection face occurs.

In the piezoelectric element described in Patent Document 2, theelectrodes and the conductive members are connected on a surface of thepiezoelectric element on which the electrodes are provided. Vibration ofthe piezoelectric element deforms the connection face and generates astress therein. As a result, the connected portion between theelectrodes and the conductive members is subjected to a stress, andthere is a probability that peeling of the connection face occurs.

An object of the disclosed technology may be to provide an ultrasonicactuator in which generation of a stress is prevented in the connectionface of the piezoelectric element between the electrodes and theconductive members.

The above-described object is accomplished by an ultrasonic actuatorwhich includes the following elements. The ultrasonic actuator includesa piezoelectric element and an electric connection member electricallyconnected to the piezoelectric element. The piezoelectric elementincludes: a plurality of generally rectangular piezoelectric layers; apower supply electrode provided on a principal surface of at least oneof the plurality of piezoelectric layers; a counter electrode providedto face the power supply electrode with the piezoelectric layerinterposed therebetween; a power supply external electrode provided onone of external surfaces of the piezoelectric element which isperpendicular to the principal surface of the piezoelectric layer andwhich is parallel to short sides of the principal surface, the powersupply external electrode being electrically coupled to the power supplyelectrode; and a counter external electrode provided on one of theexternal surfaces of the piezoelectric element which is perpendicular tothe principal surface of the piezoelectric layer and which is parallelto the short sides of the principal surface, the counter externalelectrode being electrically coupled to the counter electrode. Theelectric connection member includes a power supply conductive memberelectrically connected to the power supply external electrode, and acounter conductive member electrically connected to the counter externalelectrode.

The disclosed technology may provide an ultrasonic actuator in whichgeneration of a stress is prevented in the connection face of thepiezoelectric element between the electrodes and the conductive members.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general perspective view of an ultrasonic actuator accordingto embodiment 1.

FIG. 2 is an orthographic developed view of a piezoelectric element P1according to embodiment 1.

FIG. 3 shows the layers of the piezoelectric element of embodiment 1which are seen in the layer stacking direction.

FIG. 4 illustrates the four regions over a principal surface of apiezoelectric layer.

FIG. 5 shows the positional relationship for connection of flexiblecables F1 and short-side surfaces of the piezoelectric element P1.

FIG. 6 is a concept diagram illustrating the displacement of the firstmode stretching vibration of the ultrasonic actuator.

FIG. 7 is a concept diagram illustrating the displacement of the secondmode bending vibration of the ultrasonic actuator.

FIG. 8 is a concept diagram illustrating the operation of the ultrasonicactuator.

FIG. 9 is an orthographic developed view of the piezoelectric element P2according to embodiment 2.

FIG. 10 shows the layers of the piezoelectric element P2 of embodiment 2which are seen in the layer stacking direction.

FIG. 11 shows the positional relationship for connection of flexiblecables F2 and short-side surfaces of the piezoelectric element P2.

FIG. 12 is an orthographic developed view of the piezoelectric elementP3 according to embodiment 3.

FIG. 13 shows the layers of the piezoelectric element P3 of embodiment 3which are seen in the layer stacking direction.

FIG. 14 shows the positional relationship for connection of flexiblecables F2 and short-side surfaces of the piezoelectric element P3.

FIG. 15 is an orthographic developed view of the piezoelectric elementP4 according to embodiment 4.

FIG. 16 shows the layers of the piezoelectric element P4 of embodiment 4which are seen in the layer stacking direction.

FIG. 17 shows the positional relationship for connection of flexiblecables F4 and short-side surfaces of the piezoelectric element P4.

FIG. 18 is an orthographic developed view of the piezoelectric elementP5 according to embodiment 5.

FIG. 19 shows the layers of the piezoelectric element P5 of embodiment 5which are seen in the layer stacking direction.

FIG. 20 shows the positional relationship for connection of flexiblecables F5 and short-side surfaces of the piezoelectric element P5.

FIG. 21 shows another ultrasonic actuator embodiment.

FIG. 22 shows still another ultrasonic actuator embodiment.

DESCRIPTION OF REFERENCE CHARACTERS

-   -   P1, P2, P3, P4, P5 piezoelectric element    -   F1, F2, F4, F5 flexible cable (electrical connection member)    -   F11, F21, F41, F51 first flexible cable (first electrical        connection member)    -   F12, F22, F42, F52 second flexible cable (second electrical        connection member)    -   1 piezoelectric layer    -   2 power supply electrode    -   2A first power supply electrode    -   2B second power supply electrode    -   2 a first power supply lead electrode    -   2 b second power supply lead electrode    -   3 counter electrode    -   3 g counter lead electrode    -   3A first counter electrode    -   3B first counter electrode    -   3 a first counter lead electrode    -   3 b second counter lead electrode    -   4 power supply external electrode    -   4A first power supply external electrode    -   4B second power supply external electrode    -   5 counter external electrode    -   5A first counter external electrode    -   5B second counter external electrode    -   6 electric line (power supply conductive member)    -   6A electric line (first power supply conductive member)    -   6B electric line (second power supply conductive member)    -   7 electric line (counter conductive member)    -   7A electric line (first counter conductive member)    -   7B electric line (second counter conductive member)    -   8 driver element    -   9 movable element    -   J1 first connection electrode    -   J2 second connection electrode    -   J3 third connection electrode    -   J4 fourth connection electrode    -   10A first connection external electrode    -   10B second connection external electrode    -   10C third connection external electrode    -   10D fourth connection external electrode    -   11 case    -   13 a, 13 b, 13 c supporting portion

DETAILED DESCRIPTION

Hereinafter, embodiments are described in detail with reference to thedrawings. Note that, in the description of the embodiments, elementswith the same reference character are identical elements. Thedescription of the elements provided with the same reference characteris sometimes omitted.

<<Embodiment 1 >>

FIG. 1 is a general perspective view of a drive unit according to thisembodiment. The drive unit of this embodiment includes an ultrasonicactuator, a movable element 9 which is actuated in a predeterminedmovable direction by the ultrasonic actuator, and a drive power supply(not shown) configured to control the ultrasonic actuator.

<1.1: General Configuration of Ultrasonic Actuator>

The ultrasonic actuator of this embodiment includes a piezoelectricelement P1, driver elements 8 provided to the piezoelectric element P1,a case 11 containing the piezoelectric element P1, supporting portions13 a-13 c supporting the piezoelectric element P1 on the case 11, andflexible cables F1 for powering the piezoelectric element P1. Generationof stretching vibration and bending vibration in the piezoelectricelement P1 causes generation of relative driving force between thepiezoelectric element P1 and the movable element 9.

As shown in FIG. 1, the ultrasonic actuator includes the piezoelectricelement P1 which is in the shape of a generally rectangularparallelepiped (for example, length 6.0 mm ×width 1.7 mm×thickness 2.0mm). The piezoelectric element P1 includes piezoelectric layers andelectrode layers which are stacked in the direction perpendicular to theplane of FIG. 1. In FIG. 1, the anterior surface of the piezoelectricelement P1 in the drawing sheet is a principal surface of thepiezoelectric layer 1. Hereinafter, a pair of opposite principalsurfaces of the piezoelectric layer are referred to as “principalsurfaces”. A pair of opposite surfaces which are perpendicular to theprincipal surfaces and which are parallel to the long sides of theprincipal surfaces are referred to as “long-side surfaces”. A pair ofopposite surfaces which are perpendicular to the principal surfaces andwhich are parallel to the short sides of the principal surfaces arereferred to as “short-side surfaces”. The principal surfaces, thelong-side surfaces and the short-side surfaces constitute the outersurfaces of the piezoelectric element P1. The long-side surfaces and theshort-side surfaces constitute the circumferential surfaces of thepiezoelectric element P1. In this embodiment, among the principalsurfaces, the long-side surfaces and the short-side surfaces, theprincipal surfaces have the largest area. In this embodiment, thepiezoelectric element P1 forms a vibrator.

The piezoelectric element P1 is contained in the case 11 which is asupporting body. The piezoelectric element P1 is supported on the case11 via three supporting portions 13 a, 13 b and 13 c. All of the threesupporting portions 13 a, 13 b and 13 c are elastic. The supportingportions 13 a and 13 c are compressed in the gaps between the twoshort-side surfaces and the case 11. In this way, the piezoelectricelement P1 is supported by the supporting portions 13 a and 13 c in thelong-side direction of the principal surface.

The two short-side surfaces of the piezoelectric element P1 areelectrically connected to electrical connection members.

One of the long-side surfaces of the piezoelectric element P1 isprovided with the driver elements 8, and the driver elements 8 are incontact with the movable element 9 which is in the shape of a flatplate. Specifically, the driver elements 8 are fixed to part of thepiezoelectric element P1 near the antinode of the second mode bendingvibration, which will be described later. The driver elements 8 are inthe shape of a circular pole and are in line contact with thepiezoelectric element P1. The driver elements 8 and the piezoelectricelement P1 are fixed together by an adhesive. The adhesive used issofter than the piezoelectric layer 1 and the driver elements 8. Thesoftness can be compared by, for example, the modulus of elasticity. Thedriver elements 8 and part of the movable element 9 which is in contactwith the driver elements 8 are formed of a ceramic material containing,e.g., zirconia, alumina, silicon nitride as main constituents, or aresin material.

The supporting portion 13 b is provided between the other long-sidesurface of the piezoelectric element P1, i.e., a long-side surfaceopposite to the long-side surface on which the driver elements 8 areprovided, and the case 11. The supporting portion 13 b is compressedalong a direction toward the movable element 9 (the lateral direction ofthe piezoelectric element P1). The supporting portion 13 b pushes thepiezoelectric element P1 against the movable element 9 due to itsreaction force. This increases the frictional force between the tips ofthe driver elements 8 and the movable element 9 so that the drivingforce produced by the vibration of the piezoelectric element P1 iseffectively transmitted to the movable element 9 via the driver elements8.

<1.2: Piezoelectric Element P1>

The piezoelectric element P1 of this embodiment is in the shape of agenerally rectangular parallelepiped. The piezoelectric element P1includes a plurality of generally rectangular piezoelectric layers 1,which are piezoelectric, and internal electrode layers interposedbetween the piezoelectric layers 1. The piezoelectric element P1 isconfigured in such a manner that the piezoelectric layers and theelectrode layers are stacked in a direction from front to back of thedrawing sheet of FIG. 1 (hereinafter, sometimes referred to as thicknessdirection).

FIG. 2 is an orthographic developed view of the piezoelectric element P1of this embodiment. In FIG. 2, a portion at the center represents theprincipal surface, portions on the right and left sides of the principalsurface are the short-side surfaces, and portions on the upper and lowersides of the principal surface are the long-side surfaces. The internalelectrode layers are located behind the principal surface, and thuscannot be seen. The positions of the internal electrode layers projectedover the principal surface are represented by broken lines. FIG. 3 showsthe respective layers of the piezoelectric element P1 of this embodimentwhich are seen in the stacking direction.

As shown in FIG. 2, the piezoelectric element P1 is in the shape of agenerally rectangular parallelepiped, which is formed by alternatelystacking the generally rectangular piezoelectric layers 1 and theinternal electrode layers. The piezoelectric layer 1 is an insulationlayer formed of, for example, a ceramic material, such as lead zirconatetitanate. The internal electrode layers are formed of power supplyelectrodes 2 and counter electrodes 3 which are alternately provided inthe stacking direction (thickness direction of the piezoelectric elementP1) with the piezoelectric layers 1 interposed therebetween. Theinternal electrode layers are electrode layers which are formed of ametal containing, for example, silver and palladium as main constituentsand which are provided on the principal surface of the piezoelectriclayer 1.

As shown in FIG. 2, power supply external electrodes 4 and counterexternal electrodes 5 are provided on the short-side surfaces of thepiezoelectric element P1. Specifically, the power supply externalelectrodes 4 include two first power supply external electrodes 4A andtwo second power supply external electrodes 4B which are mutuallyseparate. The first power supply external electrodes 4A are provided onrespective one of the two short-side surfaces of the piezoelectricelement P1 at one lateral end of the piezoelectric element P1. Thesecond power supply external electrodes 4B are provided on respectiveone of the two short-side surfaces of the piezoelectric element P1 atthe other lateral end of the piezoelectric element P1 (i.e., the lateralend opposite to the first power supply external electrode 4A). Thepiezoelectric element P1 includes the two counter external electrodes 5.The counter external electrodes 5 are provided respectively on the twoshort-side surfaces of the piezoelectric element P1 at the lateralcenter of the piezoelectric element P1 (i.e., between the first powersupply external electrode 4A and the second power supply externalelectrodes 4B). These electrodes 4A, 4B and 5 are mutually insulated. Inother words, the electrodes 4A, 4B and 5 are not electrically coupled toone another.

The power supply electrodes 2 are provided on a principal surface of atleast one of the plurality of piezoelectric layers 1 as shown in FIG.3(B).

Specifically, the power supply electrodes 2 include, on the sameprincipal surface of the piezoelectric layer 1, two first power supplyelectrodes 2A and two second power supply electrodes 2B which are notelectrically coupled to the first power supply electrodes 2A. The firstpower supply electrodes 2A and the second power supply electrodes 2B arerectangular electrodes.

Among four divisional regions A1-A4 (see FIG. 4) of the principalsurface of the piezoelectric layer 1 which are defined by halving theprincipal surface with respect to both longitudinal direction L andlateral direction S, the first power supply electrodes 2A are providedin two of the four divisional regions which are aligned in the firstdiagonal direction D1 of the principal surface of the piezoelectriclayer 1, i.e., in the divisional regions A2 and A4. The second powersupply electrodes 2B are provided in the other two of the fourdivisional regions A1-A4 which are aligned in the second diagonaldirection D2 of the principal surface of the piezoelectric layer 1,i.e., in the divisional regions A1 and A3.

Each of the first power supply electrodes 2A includes a first powersupply lead electrode 2 a extending to the first power supply externalelectrode 4A which is provided on a closer one of the two short-sidesurfaces of the piezoelectric element P1. In this way, the first powersupply electrode 2A is electrically coupled to the first power supplyexternal electrode 4A via the first power supply lead electrode 2 a. Thefirst power supply electrodes 2A which are provided in the same region(A2 or A4) on the principal surfaces of different piezoelectric layers 1are electrically coupled to each other via the first power supply leadelectrodes 2 a and the first power supply external electrode 4A.

Each of the second power supply electrodes 2B includes a second powersupply lead electrode 2 b extending to the second power supply externalelectrode 4B which is provided on a closer one of the two short-sidesurfaces of the piezoelectric element P1. In this way, the second powersupply electrode 2B is electrically coupled to the second power supplyexternal electrode 4B via the second power supply lead electrode 2 b.The second power supply electrodes 2B which are provided in the sameregion (A1 or A3) on the principal surfaces of different piezoelectriclayers 1 are electrically coupled to each other via the second powersupply lead electrodes 2 b and the second power supply externalelectrode 4B.

The counter electrode 3 is provided over substantially the entiresurface of the piezoelectric layer 1 as shown in FIG. 3(D).Specifically, the counter electrode 3 is not provided in acircumferential region of the principal surface of the piezoelectriclayer 1 but is provided over substantially the entirety of a regioninside the circumferential region. The counter electrode 3 includescounter lead electrodes 3 g which extend from its lateral center to thecounter external electrodes 5 which are provided on both short-sidesurfaces of the piezoelectric element P1. In this way, the counterelectrode 3 is electrically coupled to the counter external electrodes 5via the counter lead electrodes 3 g. The counter electrodes 3 providedon different piezoelectric layers 1 are electrically coupled to eachother via the counter lead electrodes 3 g and the counter externalelectrodes 5.

The piezoelectric element P1 is formed by stacking the piezoelectriclayers 1 provided with the power supply electrodes 2 or the counterelectrode 3 on the principal surfaces as described above. Specifically,the plurality of piezoelectric layers 1 are sequentially stacked in theorder of the piezoelectric layer 1 provided with the power supplyelectrodes 2, the piezoelectric layer 1 provided with the counterelectrode 3, the piezoelectric layer 1 provided with the power supplyelectrodes 2, . . . The piezoelectric layers 1 are stacked such that theprincipal surfaces provided with the power supply electrodes 2 or thecounter electrode 3 are oriented in the same direction, i.e., such thatthe principal surface of one of the piezoelectric layers 1 on which thepower supply electrodes 2 or the counter electrode 3 is provided facethe principal surface of another one of the piezoelectric layers 1 onwhich none of the power supply electrodes 2 and the counter electrode 3is provided. Note that, the first and/or last of the stacked layers arethe piezoelectric layers 1 which are not provided with the power supplyelectrodes 2 or the counter electrode 3 such that the power supplyelectrodes 2 or the counter electrode 3 would not be exposed.

As a result of stacking the piezoelectric layers 1, the power supplyelectrodes 2 and the counter electrode 3, each of the piezoelectriclayers 1 is sandwiched by the power supply electrodes 2 (specifically,the first power supply electrode 2A and the second power supplyelectrode 2B) and the counter electrode 3. Here, each of thepiezoelectric layers 1 is polarized from the power supply electrode 2side to the counter electrode 3 side.

In the thus-stacked structure, the power supply electrodes 2 and thecounter electrode 3 are overlapping with each other with thepiezoelectric layer 1 interposed therebetween when seen in the stackingdirection. However, the piezoelectric layers 1 include a region in whichthe power supply electrodes 2 and the counter electrode 3 are notoverlapping when seen in the stacking direction (see FIG. 2). Forexample, the first power supply lead electrode 2 a, the second powersupply lead electrode 2 b, and the counter lead electrodes 3 g are notoverlapping with the counter electrode 3 or the power supply electrodes2 when seen in the stacking direction. In part of the piezoelectriclayers 1 corresponding to the non-overlapping region, no electric fieldoccurs. In other words, this part of the piezoelectric layers 1 ispiezoelectrically inactive. Specifically, in part of the piezoelectriclayers 1 near the short-side surfaces, the power supply electrodes 2 andthe counter electrode 3 are not overlapping when seen in the stackingdirection. This part of the piezoelectric layers 1 is piezoelectricallyinactive.

The resonance frequency of the stretching vibration and the resonancefrequency of the bending vibration of the piezoelectric element P1,which will be described later, depend on the material, the shape, etc.,of the piezoelectric element P1. The material, the shape, etc., of thepiezoelectric element P1 are determined such that the resonancefrequency of the stretching vibration and the resonance frequency of thebending vibration are approximately equal to each other.

<1.3: Electrical Connection Member>

In this embodiment, flexible cables F1 are used as the electricalconnection member. The flexible cables F1 include a first flexible cableF11 and a second flexible cable F12. As shown in FIG. 1, the firstflexible cable F11 and the second flexible cable F12 are electricallyconnected to the respective short-side surfaces of the piezoelectricelement P1. The first flexible cable F11 and the second flexible cableF12 are electrically coupled to the piezoelectric element P1. The firstflexible cable F11 and the second flexible cable F12 have substantiallythe same shape.

FIG. 5 shows the positional relationship in connection between the firstand second flexible cables F11 and F12 and the lateral surfaces of thepiezoelectric element P1. As shown in FIG. 5, the first and secondflexible cables F11 and F12 include a plurality of electric wires formedby printing copper over an insulative resin substrate. The electricwires are mutually insulated.

The first flexible cable F11 is connected to one of the short-sidesurfaces of the piezoelectric element P1. The second flexible cable F12is connected to the other one of the short-side surfaces of thepiezoelectric element P1. The first flexible cable F11 and the secondflexible cable F12 each have electric lines 6 which are connected to thepower supply external electrodes 4 and an electric line 7 which isconnected to the counter external electrodes 5. Specifically, the firstflexible cable F11 and the second flexible cable F12 each have anelectric line 6A which is coupled to the first power supply externalelectrode 4A, an electric line 6B which is coupled to the second powersupply external electrode 4B, and an electric line 7 which is coupled tothe counter external electrodes 5. In the first flexible cable F11, theelectric line 6A, the electric line 7 and the electric line 6B aresequentially arranged from one lateral end to the other lateral end ofthe piezoelectric element P1. In the second flexible cable F12, theelectric line 6B, the electric line 7 and the electric line 6A aresequentially arranged from the one lateral end to the other lateral endof the piezoelectric element P1. The electric lines 6 constitute thepower supply conductive member. The electric line 7 constitutes thecounter conductive member. More specifically, the electric line 6Aconstitutes the first power supply conductive member, and the electricline 6B constitutes the second power supply conductive member.

The first flexible cable F11 has a shape symmetrical about a plane whichpasses through the midpoints of the short sides of the principal planeof the piezoelectric layer 1 and which is perpendicular to theshort-side surfaces. The second flexible cable F12 also has a shapesymmetrical about the plane which passes through the midpoints of theshort sides of the principal plane of the piezoelectric layer 1 andwhich is perpendicular to the short-side surfaces as does the firstflexible cable F11. The first flexible cable F11 and the second flexiblecable F12 have a shape symmetrical about a plane which passes throughthe midpoints of the long sides of the principal plane of thepiezoelectric layer 1 and which is perpendicular to the principalsurface. A connecting portion of the first flexible cable F11 which isconnected to the piezoelectric element P1 has a shape symmetrical aboutthe plane which passes through the midpoints of the short sides of theprincipal plane of the piezoelectric layer 1 and which is perpendicularto the short-side surfaces. Also, a connecting portion of the secondflexible cable F12 which is connected to the piezoelectric element P1has a shape symmetrical about the plane which passes through themidpoints of the short sides of the principal plane of the piezoelectriclayer 1 and which is parallel to the long-side surfaces. The connectingportion of the first flexible cable F11 which is connected to thepiezoelectric element P1, and the connecting portion of the secondflexible cable F12 which is connected to the piezoelectric element P1have a shape symmetrical about the plane which passes through themidpoints of the long sides of the principal plane of the piezoelectriclayer 1 and which is parallel to the short-side surface.

In the connecting portions of the first and second flexible cables F11and F12, and a connecting portion of the piezoelectric element P1, theseelements are electrically connected and adhered using an anisotropicconductive adhesion sheet. The anisotropic conductive adhesion sheet isprepared by molding a resin containing electrically conductive particlesdispersed therein into the form of a sheet, respectively. Theanisotropic conductive adhesion sheet has an electric conductivity inthe adhesion direction, i.e., in the sheet thickness direction, butlacks electric conductivity in the in-plane directions. Therefore, theplurality of electrodes provided over the short-side surfaces of thepiezoelectric element P1 can be electrically connected to the respectiveelectric lines of the first and second flexible cables F11 and F12 by asingle anisotropic conductive adhesion sheet with the electrodes beingmutually insulated. In the first step of the connection method, ananisotropic conductive sheet is sandwiched between the first and secondflexible cables F11 and F12 made of polyimide and the piezoelectricelement P1. Then, the first and second flexible cables F11 and F12 arepressed against the piezoelectric element P1 using a heated flat iron.As a result, the first and second flexible cables F11 and F12 and thepiezoelectric element P1 are electrically coupled by the electricallyconductive particles and adhered by the effect of the resin of theanisotropic conductive adhesion sheet.

The connection portions of the first and second flexible cables F11 andF12 and the piezoelectric element P1 are respectively interposed betweenthe supporting portion 13 a and the piezoelectric element P1 and betweenthe supporting portion 13 c and the piezoelectric element P1.Specifically, the first flexible cable F11 is pressed by the supportingportion 13 a against the piezoelectric element P1. The second flexiblecable F12 is pressed by the supporting portion 13 c against thepiezoelectric element P1.

The electric lines 6 connected to the power supply external electrodes 4are an example of the power supply conductive member. The electric line6A connected to the first power supply external electrode 4A is anexample of the first power supply conductive member. The electric line6B connected to the second power supply external electrode 4B is anexample of the second power supply conductive member. The electric lines7 connected to the counter external electrodes 5 are an example of thecounter conductive member. The first flexible cable F11 is an example ofthe first electrical connection member. The second flexible cable F12 isan example of the second electrical connection member.

The first and second flexible cables F11 and F12 are coupled to a powersupply (not shown). A driving voltage from the power supply is appliedto the piezoelectric element P1 via the first and second flexible cablesF11 and F12 such that vibration is generated in the piezoelectricelement P1.

<1.4: Operation of Ultrasonic Actuator>

Hereinafter, an operation of the ultrasonic actuator is described. FIG.6 is a concept diagram illustrating the displacement of the first-orderstretching vibration according to this embodiment. FIG. 7 is a conceptdiagram illustrating the displacement of the second-order bendingvibration of the ultrasonic actuator. FIG. 8 is a concept diagramillustrating the operation of the piezoelectric element P1. Note that,in FIGS. 6-8, the principal surface of the piezoelectric element P1 isparallel to the surfaces of the sheets of the drawings.

The electric lines 7 of the flexible cables F11 and F12 are coupled tothe ground. The power supply applies a sinusoidal driving voltage of apredetermined frequency, as the first driving voltage, to the firstpower supply electrode 2A of the principal surface of the piezoelectriclayer 1 via the electric line 6A and the first power supply externalelectrode 4A. Also, the power supply also applies a sinusoidal seconddriving voltage to the second power supply electrode 2B via the electricline 6B and the second power supply external electrode 4B. The amplitudeand frequency of the second driving voltage are substantially equal tothose of the first driving voltage. The frequencies of the first andsecond driving voltages are set near the resonance frequency of thestretching vibration and the resonance frequency of the bendingvibration of the piezoelectric element P1 which are substantially equalto each other.

When the phase difference between the first driving voltage applied tothe first power supply electrode 2A and the second driving voltageapplied to the second power supply electrode 2B is 0°, the first-orderstretching vibration is induced in the piezoelectric element P1 as shownin FIG. 6. When the phase difference is 180°, the second-order bendingvibration is induced in the piezoelectric element P1 as shown in FIG. 7.

When the phase difference between the first driving voltage applied tothe first power supply electrode 2A and the second driving voltageapplied to the second power supply electrode 2B is generally 90° or−90°, the first-order stretching vibration and the second-order bendingvibration are harmonically induced in the piezoelectric element P1 asshown in FIG. 8. As a result, the piezoelectric element P1 vibrates withits shape being sequentially deformed in the order of FIG. 8(A), FIG.8(B), FIG. 8(C), and FIG. 8(D). The driver elements 8 provided on thepiezoelectric element P1 make a revolutionary movement, specifically agenerally-elliptic movement, when seen in the direction perpendicular tothe surface of the sheet of FIG. 8. In other words, the compositevibration of the stretching vibration and bending vibration of thepiezoelectric element P1 causes the driver elements 8 to make anelliptic movement. Due to this elliptic movement, the movable element 9on which the driver elements 8 abut moves relative to the piezoelectricelement P1.

The piezoelectric element P1 is arranged such that the longitudinaldirection of its principal surface is equal to the movable direction ofthe movable element 9, and that the lateral direction of its principalsurface is equal to the direction in which the piezoelectric element P1is biased by the supporting portion 13 b toward the movable element 9.The stretching direction of the stretching vibration of thepiezoelectric element P1 is equal to the movable direction of themovable element 9, and the vibration direction of the bending vibrationis equal to the direction in which the driver elements 8 are pressedagainst the movable element 9. Note that the stacking direction of thepiezoelectric element P1 is perpendicular to both the stretchingdirection of the stretching vibration and the vibration direction of thebending vibration.

The short-side surfaces of the piezoelectric element P1 are far awayfrom a stress-concentrated part of the stretching vibration andtherefore create only a small stress. Since the short-side surfaces arefree ends of the piezoelectric element P1, only a small stress iscreated even in the case of the bending vibration. In this embodiment,the first and second flexible cables F11 and F12 are connected to theshort-side surfaces. Therefore, the stress created in the connectionfaces (connection portions) by vibration of the piezoelectric element isreduced. Thus, occurrence of peeling at the connection faces can beprevented. In this embodiment, the connection faces of the piezoelectricelement P1 and the first and second flexible cables F11 and F12 includeconnection faces of the piezoelectric element P1 and the anisotropicconductive adhesion sheets and connection faces of the anisotropicconductive adhesion sheets and the first and second flexible cables F11and F12.

<1.5: Advantages of Embodiment>

In this embodiment, the short-side surfaces of the piezoelectric elementP1 are far away from a stress-concentrated part of the first modestretching vibration and therefore create only a small stress. Since thelateral surfaces are free ends of the piezoelectric element, only asmall stress is created even in the case of the second mode bendingvibration. In view of such circumstances, the flexible cables F1, whichare the electrical connection members, are connected to the short-sidesurfaces of the piezoelectric element P1, so that the stress created inthe connection faces of the flexible cables F1 and the piezoelectricelement P1 by vibration of the piezoelectric element P1 is reduced.Thus, occurrence of peeling at the connection faces of the piezoelectricelement P1 and the flexible cables F1 can be prevented. In other words,the electrical connection members are connected to the short-sidesurfaces of the piezoelectric element P1 which maintain themselvessubstantially flat even in the first mode stretching vibration and inthe second mode bending vibration, whereby stress is unlikely to occurin the planes of the electrical connection members, and stableconnection can be realized.

When seen in a direction perpendicular to the principal surface of thepiezoelectric element P1, an area of the power supply electrodes 2 andan area of the counter electrode 3 are not overlapping in regions nearthe short sides of the principal surface of the piezoelectric layer 1.Therefore, part of the piezoelectric layer 1 near the short sides of itsprincipal surface is piezoelectrically inactive, and occurrence ofstrain due to electrostrictive effect is reduced. Since the stresscreated in the connection faces of the electrical connection members andthe piezoelectric element P1 by vibration of the piezoelectric elementis reduced by connecting the electrical connection members to theshort-side surfaces of the piezoelectric element P1, occurrence ofpeeling at the connection faces can be prevented. When the piezoelectricelement P1 and the electrical connection members are connected byheating, such heating can result in reduced polarization of thepiezoelectric layer 1 near the short-side surfaces of the piezoelectricelement P1. Collapse of the balance of polarization near the twoshort-side surfaces leads to collapse of the vibration balance. However,since the part of the piezoelectric element P1 near the short-sidesurfaces piezoelectrically inactive as described above, collapse of thebalance of vibration of the piezoelectric element P1 can be preventedeven if the state of polarization of the piezoelectric layer 1 isaltered by the heat applied for connection of the electrical connectionmembers. Examples of the thermal connection of the piezoelectric elementP1 and the electrical connection members by heating include connectionwith an anisotropic conductive adhesive sheet as in the above-describedembodiment as well as connection with a conductive adhesive, alow-melting metal, etc.

The electrical connection members include the first electricalconnection member and the second electrical connection member. The firstelectrical connection member is electrically connected to thepiezoelectric element P1 at one of the two short-side surfaces which areperpendicular to the principal surface of the piezoelectric layer 1 andwhich are parallel to the short sides of the principal surface. Thesecond electrical connection member is electrically connected to thepiezoelectric element P1 at the other short-side surface. The shape ofthe first electrical connection member is symmetrical about a planewhich passes through the midpoints of the short sides of the principalsurface of the piezoelectric layer 1 and which is perpendicular to theone of the two lateral surfaces. The shape of the second electricalconnection member is symmetrical about a plane which passes through themidpoints of the short sides of the principal surface of thepiezoelectric layer 1 and which is perpendicular to the other one of thetwo lateral surfaces. In this configuration, the influence of theconnection of the electrical connection members on vibration issymmetrical about a plane which passes through the midpoints of theshort sides of the principal surface of the piezoelectric layer andwhich is perpendicular to the short-side surfaces. The influence of theconnection of the electrical connection members on the symmetry ofvibration can be reduced. As a result, the vibration balance of thepiezoelectric element can be improved.

The first electrical connection member and the second electricalconnection member are shaped symmetrical about a plane which passesthrough the midpoints of the long sides of the principal surface of thepiezoelectric layer 1 and which is perpendicular to the principalsurface. In this configuration, the influence of the connection of theelectrical connection members on vibration is symmetrical about a planewhich passes through the midpoints of the long sides of the principalsurface of the piezoelectric layer 1 and which is perpendicular to theprincipal surface. The influence of the connection of the electricalconnection members on the symmetry of vibration can be reduced.

Since the driver elements 8 and the piezoelectric element P1 are fixedlyin point contact or line contact with each other, interference with thebending vibration of the piezoelectric element P1 can be reduced, andthe efficiency of the bending vibration can be improved.

<<Embodiment 2 >>

An ultrasonic actuator according to embodiment 2 of the presentinvention is now described. Note that elements equivalent to thosedescribed in the above embodiment are denoted by the same referencecharacters, and the description thereof is herein omitted. Theultrasonic actuator of embodiment 2 is different from embodiment 1 inthe configurations of the piezoelectric element and the flexible cables.

<2.1: Piezoelectric Element P2>

The piezoelectric element P2 of this embodiment is in the shape of agenerally rectangular parallelepiped. The piezoelectric element P2includes a plurality of generally rectangular piezoelectric layers 1,and internal electrode layers interposed between the piezoelectriclayers 1. The piezoelectric element P2 includes the piezoelectric layersand the electrode layers which are stacked in a direction from front toback of the drawing sheet of FIG. 1.

FIG. 9 is an orthographic developed view of the piezoelectric elementP2. FIG. 10 shows the respective layers of the piezoelectric element P2which are seen in the stacking direction.

As shown in FIG. 9, the piezoelectric element P2 is in the shape of agenerally rectangular parallelepiped, which is formed by alternatelystacking the generally rectangular piezoelectric layers 1 and theinternal electrode layers. The piezoelectric layer 1 is an insulationlayer formed of, for example, a ceramic material, such as lead zirconatetitanate. The internal electrode layers are formed of power supplyelectrodes 2 and counter electrodes 3 which are alternately provided inthe stacking direction (thickness direction of the piezoelectric elementP2) with the piezoelectric layers 1 interposed therebetween. In FIG. 9,a portion at the center represents the principal surface, portions onthe right and left sides of the principal surface are the short-sidesurfaces, and portions on the upper and lower sides of the principalsurface are the long-side surfaces. The internal electrode layers arebehind the principal surface and thus cannot be seen. The positions ofthe internal electrode layers projected over the principal surface arerepresented by broken lines.

As shown in FIG. 9, power supply external electrodes 4 and counterexternal electrodes 5 are provided on the short-side surfaces of thepiezoelectric element P2. Specifically, the power supply externalelectrodes 4 include a first power supply external electrode 4A and asecond power supply external electrode 4B which are mutually separate.The first power supply external electrode 4A and the second power supplyexternal electrode 4B are provided on one of the two short-side surfacesof the piezoelectric element P2. The piezoelectric element P2 includesthe two counter external electrodes 5 which are provided on the otherone of the two short-side surfaces. These electrodes 4A, 4B and 5 aremutually insulated. In other words, the electrodes 4A, 4B and 5 are notelectrically coupled to one another.

The power supply electrodes 2 are provided on the principal surface ofat least one of the plurality of piezoelectric layers 1 as shown in FIG.10(B) and FIG. 10(C). Specifically, the power supply electrodes 2 areprovided on the principal surface of at least one of the plurality ofpiezoelectric layers 1 in the first pattern as shown in FIG. 10(B). Onthe principal surface of another one of the plurality of piezoelectriclayers 1 different from the piezoelectric layer 1 on which the powersupply electrodes 2 are provided in the first pattern, the power supplyelectrodes 2 are provided in the second pattern as shown in FIG. 10(C)which is different from the first pattern.

The power supply electrodes 2 include first power supply electrodes 2Awhich are provided on the principal surface of one of the piezoelectriclayers 1 and second power supply electrodes 2B which are provided on theprincipal surface of another one of the plurality of piezoelectriclayers 1 different from the piezoelectric layer 1 provided with thefirst power supply electrode 2A. The first power supply electrodes 2Aand the second power supply electrodes 2B are not electrically coupledto each other.

Specifically, among four divisional regions A1-A4 (see FIG. 4) of theprincipal surface of the piezoelectric layer 1 which are defined byhalving the principal surface with respect to both longitudinaldirection L and lateral direction S, the first power supply electrodes2A are provided in two of the four divisional regions which are alignedin the first diagonal direction D1 of the principal surface of thepiezoelectric layer 1, i.e., in the divisional regions A2 and A4.Further, the power supply electrodes 2 include a first connectionelectrode J1 extending in the lateral direction at the longitudinalcenter of the principal surface of the piezoelectric layer 1. The firstpower supply electrodes 2A provided in the two divisional regions A2 andA4 are electrically connected via the first connection electrode J1. Thefirst power supply electrodes 2A and the first connection electrode J1constitute the first pattern.

The second power supply electrodes 2B are provided in the other two ofthe four divisional regions A1-A4 (see FIG. 4) which are aligned in thesecond diagonal direction D2 of the principal surface of thepiezoelectric layer 1, i.e., in the divisional regions A1 and A3.Further, the power supply electrodes 2 include a second connectionelectrode J2 extending in the lateral direction at the longitudinalcenter of the principal surface of the piezoelectric layer 1. The secondpower supply electrodes 2B provided in the two divisional regions A1 andA3 are electrically coupled via the second connection electrode J2. Thesecond power supply electrodes 2B and the second connection electrode J2constitute the second pattern.

Among the first power supply electrodes 2A provided in the twodivisional regions A2 and A4, the first power supply electrode 2Aprovided in the divisional region A2 which is closer to the short-sidesurface that has the first power supply external electrode 4A thereonincludes a first power supply lead electrode 2 a extending to the firstpower supply external electrode 4A. In this way, the first power supplyelectrode 2A of the divisional region A2 is electrically coupled to thefirst power supply external electrode 4A via the first power supply leadelectrode 2 a. The first power supply electrodes 2A of differentpiezoelectric layers 1 are electrically coupled to each other via thefirst power supply external electrode 4A, the first power supply leadelectrodes 2 a, and the first connection electrodes J1.

In each of the first and second patterns, among the second power supplyelectrodes 2B provided in the two divisional regions A1 and A3, thesecond power supply electrode 2B provided in the divisional region A3which is closer to the short-side surface that has the second powersupply external electrode 4B thereon includes a second power supply leadelectrode 2 b extending to the second power supply external electrode4B. In this way, the second power supply electrode 2B of the divisionalregion A3 is electrically coupled to the second power supply externalelectrode 4B via the second power supply lead electrode 2 b. The secondpower supply electrodes 2B of different piezoelectric layers 1 areelectrically coupled to each other via the second power supply externalelectrode 4B, the second power supply lead electrodes 2 b, and thesecond connection electrodes J2.

The counter electrode 3 is provided over substantially the entiresurface of the piezoelectric layer 1 as shown in FIG. 10(D).Specifically, the counter electrode 3 is not provided in acircumferential region of the principal surface of the piezoelectriclayer 1 but is provided over substantially the entirety of a regioninside the circumferential region. The counter electrode 3 includescounter lead electrodes 3 g which extend from both ends of a short-sidenear the short-side surface that has the counter external electrodes 5thereon toward the counter external electrodes 5 so as to be connectedto the counter external electrodes 5. In this way, the counter electrode3 is electrically coupled to the counter external electrodes 5 via thecounter lead electrodes 3 g. The counter electrodes 3 provided ondifferent piezoelectric layers 1 are electrically coupled to each othervia the counter lead electrodes 3 g and the counter external electrodes5.

The piezoelectric element P2 is formed by stacking the piezoelectriclayers 1 provided with the power supply electrodes 2 or the counterelectrode 3 on the principal surfaces as described above. Specifically,the plurality of piezoelectric layers 1 are sequentially stacked in theorder of the piezoelectric layer 1 provided with the first pattern powersupply electrodes 2 (i.e., the first power supply electrodes 2A), thepiezoelectric layer 1 provided with the counter electrode 3, thepiezoelectric layer 1 provided with the second pattern power supplyelectrodes 2 (i.e., the second power supply electrodes 2B), thepiezoelectric layer 1 provided with the counter electrode 3, thepiezoelectric layer 1 provided with the first pattern power supplyelectrodes 2, the piezoelectric layer 1 provided with the counterelectrode 3, . . . . The piezoelectric layers 1 are stacked such thatthe principal surfaces provided with the power supply electrodes 2 orthe counter electrode 3 are oriented in the same direction, i.e., suchthat the principal surface of one of the piezoelectric layers 1 on whichthe power supply electrodes 2 or the counter electrode 3 is providedface the principal surface of another one of the piezoelectric layers 1on which none of the power supply electrodes 2 and the counter electrode3 is provided. Note that, the first and/or last of the stacked layersare the piezoelectric layers 1 which are not provided with the powersupply electrodes 2 or the counter electrode 3 such that the powersupply electrodes 2 or the counter electrode 3 would not be exposed.

As a result of stacking the piezoelectric layers 1, the power supplyelectrodes 2 and the counter electrode 3, each of the piezoelectriclayers 1 is sandwiched by the power supply electrodes 2 (specifically,the first power supply electrode 2A or the second power supply electrode2B) and the counter electrode 3. Thus, when seen in the stackingdirection, the power supply electrodes 2 and the counter electrode 3 areoverlapping with each other with the piezoelectric layer 1 interposedtherebetween. Here, each of the piezoelectric layers 1 is polarized fromthe power supply electrode 2 side to the counter electrode 3 side.

However, the piezoelectric layers 1 include a region in which the powersupply electrodes 2 and the counter electrode 3 are not overlapping whenseen in the stacking direction (see FIG. 9). For example, the firstpower supply lead electrode 2 a, the second power supply lead electrode2 b, and the counter lead electrodes 3 g are not overlapping with thecounter electrode 3 or the power supply electrodes 2 when seen in thestacking direction. In part of the piezoelectric layers 1 correspondingto the non-overlapping region, no electric field occurs. In other words,this part of the piezoelectric layers 1 is piezoelectrically inactive.Specifically, in part of the piezoelectric layers 1 near the short-sidesurfaces, the power supply electrodes 2 and the counter electrode 3 arenot overlapping when seen in the stacking direction. This part of thepiezoelectric layers 1 is piezoelectrically inactive.

The resonance frequency of the stretching vibration and the resonancefrequency of the bending vibration of the piezoelectric element P2,which will be described later, depend on the material, the shape, etc.,of the piezoelectric element P2. The material, the shape, etc., of thepiezoelectric element P2 are determined such that the resonancefrequency of the stretching vibration and the resonance frequency of thebending vibration are approximately equal to each other.

<2.2: Electrical Connection Member>

In this embodiment, flexible cables F2 are used as the electricalconnection member. The flexible cables F2 include a first flexible cableF21 and a second flexible cable F22. As shown in FIG. 1, the firstflexible cable F21 and the second flexible cable F22 are electricallyconnected to the respective short-side surfaces of the piezoelectricelement P2. The first flexible cable F21 and the second flexible cableF22 are electrically coupled to the piezoelectric element P2. The firstflexible cable F21 and the second flexible cable F22 have substantiallythe same shape.

FIG. 11 shows the positional relationship in connection between thefirst and second flexible cables F21 and F22 and the lateral surfaces ofthe piezoelectric element P2. As shown in FIG. 11, the first and secondflexible cables F21 and F22 include a plurality of electric wires formedby printing copper over an insulative resin substrate. The electricwires are mutually insulated.

The first flexible cable F21 is connected to one of the short-sidesurfaces of the piezoelectric element P2. The first flexible cable F21has electric lines 6 which are connected to the power supply externalelectrodes 4. Specifically, the first flexible cable F21 has an electricline 6A connected to the first power supply external electrode 4A and anelectric line 6B connected to the second power supply external electrode4B.

The second flexible cable F22 is connected to the other one of theshort-side surfaces of the piezoelectric element P2. The second flexiblecable F22 has electric lines 7 which are connected to the counterexternal electrodes 5. Specifically, the second flexible cable F22 haselectric lines 7 connected to the counter external electrodes 5.

The first flexible cable F21 has a shape symmetrical about a plane whichpasses through the midpoints of the short sides of the principal planeof the piezoelectric layer 1 and which is perpendicular to theshort-side surfaces. The second flexible cable F22 also has a shapesymmetrical about the plane which passes through the midpoints of theshort sides of the principal plane of the piezoelectric layer 1 andwhich is perpendicular to the short-side surfaces. The first flexiblecable F21 and the second flexible cable F22 have a shape symmetricalabout a plane which passes through the midpoints of the long sides ofthe principal plane of the piezoelectric layer 1 and which isperpendicular to the principal surface. A connecting portion of thefirst flexible cable F21 which is connected to the piezoelectric elementP2 has a shape symmetrical about the plane which passes through themidpoints of the short sides of the principal plane of the piezoelectriclayer 1 and which is perpendicular to the short-side surfaces. Aconnecting portion of the second flexible cable F22 which is connectedto the piezoelectric element P2 also has a shape symmetrical about theplane which passes through the midpoints of the short sides of theprincipal plane of the piezoelectric layer 1 and which is perpendicularto the short-side surfaces. The connecting portion of the first flexiblecable F21 which is connected to the piezoelectric element P2 and theconnecting portion of the second flexible cable F22 which is connectedto the piezoelectric element P2 have a shape symmetrical about the planewhich passes through the midpoints of the long sides of the principalplane of the piezoelectric layer 1 and which is perpendicular to theprincipal surface.

In the connecting portions of the first and second flexible cables F21and F22 and a connecting portion of the piezoelectric element P2, theseelements are electrically connected and adhered using an anisotropicconductive adhesion sheet. The anisotropic conductive adhesion sheet isprepared by molding a resin containing electrically conductive particlesdispersed therein into the form of a sheet. The anisotropic conductiveadhesion sheet has an electric conductivity in the adhesion direction,i.e., in the sheet thickness direction, but lacks electric conductivityin the in-plane directions of the adhesion surface. Therefore, theplurality of electrodes provided over the short-side surfaces of thepiezoelectric element P2 can be electrically connected to the respectiveelectric lines of the first and second flexible cables F21 and F22 by asingle anisotropic conductive adhesion sheet with the electrodes beingmutually insulated. In the first step of the connection method, ananisotropic conductive sheet is sandwiched between the first and secondflexible cables F21 and F22 made of polyimide and the piezoelectricelement P2. Then, the first and second flexible cables F21 and F22 arepressed against the piezoelectric element P2 using a heated planarcautery. As a result, the first and second flexible cables F21 and F22and the piezoelectric element P2 are electrically coupled by theelectrically conductive particles and adhered by means of the resin ofthe anisotropic conductive adhesion sheet.

The connection portions of the first and second flexible cables F21 andF22 and the piezoelectric element P2 are respectively interposed betweenthe supporting portion 13 a and the piezoelectric element P2 and betweenthe supporting portion 13 c and the piezoelectric element P2.Specifically, the first flexible cable F21 is pressed by the supportingportion 13 a against the piezoelectric element P2. The second flexiblecable F22 is pressed by the supporting portion 13 c against thepiezoelectric element P2.

The electric lines 6 connected to the power supply external electrodes 4are an example of the power supply conductive member. The electric line6A connected to the first power supply external electrode 4A is anexample of the first power supply conductive member. The electric line6B connected to the second power supply external electrode 4B is anexample of the second power supply conductive member. The electric lines7 connected to the counter external electrodes 5 are an example of thecounter conductive member. The first flexible cable F21 is an example ofthe first electrical connection member. The second flexible cable F22 isan example of the second electrical connection member.

The first and second flexible cables F21 and F22 are coupled to a powersupply (not shown). A driving voltage from the power supply is appliedto the piezoelectric element P2 via the first and second flexible cablesF21 and F22 such that vibration is generated in the piezoelectricelement P2.

<2.3: Operation of Ultrasonic Actuator>

Hereinafter, an operation of the ultrasonic actuator is described. Theoperation of the ultrasonic actuator of this embodiment is basically thesame as that of the ultrasonic actuator of embodiment 1. Specifically, afirst driving voltage at a frequency near the substantially-matchedresonance frequencies of the stretching vibration and the bendingvibration of the piezoelectric element P2 is applied to the first powersupply electrode 2A, and a second driving voltage which is approximatelyequal in amplitude and frequency to and different in phase by generally90° or −90° from the first driving voltage is applied to the secondpower supply electrode 2B, whereby the first-order stretching vibrationand the second-order bending vibration are harmonically induced in thepiezoelectric element P2. As a result, the piezoelectric element P2vibrates with its shape being sequentially deformed in the order of FIG.8(A), FIG. 8(B), FIG. 8(C), and FIG. 8(D). The driver elements 8provided on the piezoelectric element P2 make an orbit movement,specifically a generally-elliptic movement, when seen in the directionperpendicular to the surface of the sheet of FIG. 8. In other words, thecomposite vibration of the stretching vibration and bending vibration ofthe piezoelectric element P2 causes the driver elements 8 to make anelliptic movement. Due to this elliptic movement, the movable element 9on which the driver elements 8 abut moves relative to the piezoelectricelement P2. In this embodiment, the first power supply externalelectrode 4A and the counter external electrodes 5 are provided atdifferent short-side surfaces. The second power supply externalelectrode 4B and the counter external electrodes 5 are provided atdifferent short-side surfaces. Therefore, a sufficient distance can beensured between the first power supply external electrode 4A and thecounter external electrodes 5 and between the second power supplyexternal electrode 4B and the counter external electrodes 5.Accordingly, sufficient insulation can be ensured between the firstpower supply external electrode 4A and the counter external electrodes 5and between the second power supply external electrode 4B and thecounter external electrodes 5.

<2.4: Advantages of Embodiment>

According to this embodiment, the first power supply external electrode4A and the counter external electrodes 5 are provided at differentshort-side surfaces. The second power supply external electrode 4B andthe counter external electrodes 5 are provided at different short-sidesurfaces. This configuration ensures a sufficient distance between thefirst power supply external electrode 4A and the counter externalelectrodes 5 and between the second power supply external electrode 4Band the counter external electrodes 5. Accordingly, sufficientinsulation can be ensured between the first power supply externalelectrode 4A and the counter external electrodes 5 and between thesecond power supply external electrode 4B and the counter externalelectrodes 5.

The principal surface of the piezoelectric layer 1 on which the firstpower supply electrode is provided has the first connection electrode J1which provides electrical connection between the first power supplyelectrodes 2A. The principal surface of another piezoelectric layer 1,which is different from the principal surface that has the firstconnection electrode J1 thereon, has the second connection electrode J2which provides electrical connection between the second power supplyelectrodes 2B. This configuration enables reduction of the number of thefirst power supply external electrodes 4A which are electrically coupledto the first power supply electrodes 2A and the number of the secondpower supply external electrodes 4B which are electrically coupled tothe second power supply electrode 2B. For example, a structure which hasthe first connection electrode J1 and the second connection electrode J2requires only one piece of the first power supply external electrode 4Aand one piece of the second power supply external electrode 4B whereasembodiment 1 which does not have the first connection electrode J1 orthe second connection electrode J2 requires two pieces of the firstpower supply external electrodes 4A and two pieces of the second powersupply external electrodes 4B. As a result, the number of connectionpoints between the piezoelectric element P2 and the electricalconnection members can be reduced, and accordingly, the probability ofoccurrence of peeling at the connection faces between the piezoelectricelement P2 and the electrical connection members. Further, the factorsof interference with the vibration of the piezoelectric element P2 aredecreased so that the efficiency of the vibration can be improved.

The longitudinal center of the piezoelectric layer 1 is the node of thefirst mode stretching vibration, i.e., a stress-concentrated part atwhich the stress caused by the stretching vibration concentrates. Inthis stress-concentrated part, electric charge concentrates due to thepiezoelectric effect. In view of such, the first connection electrode J1and the second connection electrode J2 have a shape elongated in thelateral direction at the longitudinal center of the principal surface ofthe piezoelectric layer 1. Therefore, the power supply electrodes 2 canhave an increased area at the longitudinal center of the piezoelectriclayer 1. By increasing the areas of the first connection electrode J1and the second connection electrode J2, large stretching vibration canbe induced even when the size of the piezoelectric element P2 isreduced. As a result, the efficiency of the ultrasonic actuator can beimproved.

Embodiment 2 can also provide effects and advantages substantiallyequivalent to those of embodiment 1.

<<Embodiment 3 >>

An ultrasonic actuator according to embodiment 3 of the presentinvention is now described. Note that elements equivalent to thosedescribed in the above embodiment are denoted by the same referencecharacters, and the description thereof is herein omitted. Theultrasonic actuator of embodiment 3 is different from embodiment 1 inthe configurations of the piezoelectric element and the flexible cables.

<3.1: Piezoelectric Element P3>

The piezoelectric element P3 of this embodiment is in the shape of agenerally rectangular parallelepiped. The piezoelectric element P3includes a plurality of generally rectangular piezoelectric layers 1,and internal electrode layers interposed between the piezoelectriclayers 1. The piezoelectric element P3 includes the piezoelectric layersand the electrode layers which are stacked in a direction from front toback of the drawing sheet of FIG. 1.

FIG. 12 is an orthographic developed view of the piezoelectric elementP3. FIG. 13 shows the respective layers of the piezoelectric element P3which are seen in the layer stacking direction. In FIG. 12, a portion atthe center represents the principal surface, portions on the right andleft sides of the principal surface are the short-side surfaces, andportions on the upper and lower sides of the principal surface are thelong-side surfaces. The internal electrode layers are behind theprincipal surface and thus cannot be seen. The positions of the internalelectrode layers projected over the principal surface are represented bybroken lines.

As shown in FIG. 12, power supply external electrodes 4 and counterexternal electrodes 5 are provided on the short-side surfaces of thepiezoelectric element P3. Specifically, the power supply externalelectrodes 4 include a first power supply external electrode 4A and asecond power supply external electrode 4B which are mutually separate.The first power supply external electrode 4A and the second power supplyexternal electrode 4B are provided on one of the two short-side surfacesof the piezoelectric element P3. The piezoelectric element P3 includesthe two counter external electrodes 5 which are provided on the otherone of the two short-side surfaces. These electrodes 4A, 4B and 5 aremutually insulated. In other words, the electrodes 4A, 4B and 5 are notelectrically coupled to one another. One of the long-side surfaces ofthe piezoelectric element P3 is provided with a first connectionexternal electrode 10A, and the other long-side surface is provided witha second connection external electrode 10B. The first connectionexternal electrode 10A and the second connection external electrode 10Bare mutually insulated.

The power supply electrodes 2 are provided on the principal surface ofat least one of the plurality of piezoelectric layers 1 as shown in FIG.13(B) and FIG. 13(C). Specifically, the power supply electrodes 2 areprovided on the principal surface of at least one of the plurality ofpiezoelectric layers 1 in the first pattern as shown in FIG. 13(B). Onthe principal surface of another one of the plurality of piezoelectriclayers 1 different from the piezoelectric layer 1 on which the powersupply electrodes 2 are provided in the first pattern, the power supplyelectrodes 2 are provided in the second pattern as shown in FIG. 13(C)which is different from the first pattern.

Specifically, the power supply electrodes 2 formed in the first patternand in the second pattern each include first power supply electrodes 2Aand second power supply electrodes 2B which are not electrically coupledto the first power supply electrodes 2A.

In each of the first and second patterns, among four divisional regionsA1-A4 (see FIG. 4) of the principal surface of the piezoelectric layer 1which are defined by halving the principal surface with respect to bothlongitudinal direction L and lateral direction S, the first power supplyelectrodes 2A are provided in two of the four divisional regions A1-A4which are aligned in the first diagonal direction D1 of the principalsurface of the piezoelectric layer 1, i.e., in the divisional regions A2and A4. The second power supply electrodes 2B are provided in the othertwo of the four divisional regions A1-A4 which are aligned in the seconddiagonal direction D2 of the principal surface of the piezoelectriclayer 1, i.e., in the divisional regions A1 and A3.

The first pattern power supply electrodes 2 include a first connectionelectrode J1 extending in the lateral direction at the longitudinalcenter of the principal surface of the piezoelectric layer 1. The firstpower supply electrodes 2A provided in the two divisional regions A2 andA4 of the first pattern are mutually coupled via the first connectionelectrode J1. The second pattern power supply electrodes 2 include asecond connection electrode J2 extending in the lateral direction at thelongitudinal center of the principal surface of the piezoelectric layer1. The second power supply electrodes 2B provided in the two divisionalregions A1 and A3 of the second pattern are mutually coupled via thesecond connection electrode J2.

In each of the first and second patterns, among the first power supplyelectrodes 2A provided in the two divisional regions A2 and A4, thefirst power supply electrode 2A provided in the divisional region A2which is closer to the short-side surface that has the first powersupply external electrode 4A thereon includes a first power supply leadelectrode 2 a extending to the first power supply external electrode 4A.In this way, the first power supply electrode 2A of the divisionalregion A2 is electrically coupled to the first power supply externalelectrode 4A via the first power supply lead electrode 2 a. Among thefirst power supply electrodes 2A provided in the two divisional regionsA2 and A4, the first power supply electrode 2A provided in thedivisional region A4 which is more distant from the short-side surfacethat has the first power supply external electrode 4A thereon includes afirst power supply lead electrode 2 a extending to the first connectionexternal electrode 10A provided on the long-side surface. In this way,the first power supply electrodes 2A of the divisional region A4 in thedifferent piezoelectric layers 1 are electrically coupled to each othervia the first connection external electrode 10A. Since in the firstpattern the first power supply electrode 2A of the divisional region A4is electrically coupled to the first power supply electrode 2A of thedivisional region A2 via the first connection electrode J1, the firstpower supply electrode 2A of the divisional region A4 of the secondpattern, which is electrically coupled to the first power supplyelectrode 2A of the divisional region A4 of the first pattern via thefirst connection external electrode 10A, is electrically coupled to thefirst power supply external electrode 4A of the first pattern via thefirst connection electrode J1.

In each of the first and second patterns, among the second power supplyelectrodes 2B provided in the two divisional regions A1 and A3, thesecond power supply electrode 2B provided in the divisional region A3which is closer to the short-side surface that has the second powersupply external electrode 4B thereon includes a second power supply leadelectrode 2 b extending to the second power supply external electrode4B. In this way, the second power supply electrode 2B of the divisionalregion A3 is electrically coupled to the second power supply externalelectrode 4B via the second power supply lead electrode 2 b. Among thesecond power supply electrodes 2B provided in the two divisional regionsA1 and A3, the second power supply electrode 2B provided in thedivisional region A1 which is more distant from the short-side surfacethat has the second power supply external electrode 4B thereon includesa second power supply lead electrode 2 b extending to the secondconnection external electrode 10B provided on the long-side surface. Inthis way, the second power supply electrodes 2B of the divisional regionA1 in the different piezoelectric layers 1 are electrically coupled toeach other via the second connection external electrode 10B. Since inthe second pattern the second power supply electrode 2B of thedivisional region A1 is electrically coupled to the second power supplyelectrode 2B of the divisional region A3 via the second connectionelectrode J2, the second power supply electrode 2B of the divisionalregion A1 of the first pattern, which is electrically coupled to thesecond power supply electrode 2B of the divisional region A1 of thesecond pattern via the second connection external electrode 10B, iselectrically coupled to the second power supply external electrode 4Bvia the second connection electrode J2 of the second pattern.

The counter electrode 3 is provided over substantially the entireprincipal surface of the piezoelectric layer 1 as shown in FIG. 13(D).Specifically, the counter electrode 3 is not provided in acircumferential region of the principal surface of the piezoelectriclayer 1 but is provided over substantially the entirety of a regioninside the circumferential region. The counter electrode 3 includescounter lead electrodes 3 g which extend from both ends of a short-sidenear the short-side surface on which the counter external electrodes 5are provided toward the counter external electrodes 5 so as to beconnected to the counter external electrodes 5. In this way, the counterelectrode 3 is electrically coupled to the counter external electrodes 5via the counter lead electrodes 3 g. The counter electrodes 3 providedon different piezoelectric layers 1 are electrically coupled to eachother via the counter lead electrodes 3 g and the counter externalelectrodes 5.

The piezoelectric element P3 is formed by stacking the piezoelectriclayers 1 provided with the power supply electrodes 2 or the counterelectrode 3 on the principal surfaces as described above. Specifically,the plurality of piezoelectric layers 1 are sequentially stacked in theorder of the piezoelectric layer 1 provided with the first pattern powersupply electrodes 2, the piezoelectric layer 1 provided with the counterelectrode 3, the piezoelectric layer 1 provided with the second patternpower supply electrodes 2, the piezoelectric layer 1 provided with thecounter electrode 3, the piezoelectric layer 1 provided with the firstpattern power supply electrodes 2, the piezoelectric layer 1 providedwith the counter electrode 3, . . . . The piezoelectric layers 1 arestacked such that the principal surfaces provided with the power supplyelectrodes 2 or the counter electrode 3 are oriented in the samedirection, i.e., such that the principal surface of one of thepiezoelectric layers 1 on which the power supply electrodes 2 or thecounter electrode 3 is provided faces the principal surface of anotherone of the piezoelectric layers 1 on which none of the power supplyelectrodes 2 and the counter electrode 3 is provided. Note that, thefirst and/or last of the stacked layers are the piezoelectric layers 1which are not provided with the power supply electrodes 2 or the counterelectrode 3 such that the power supply electrodes 2 or the counterelectrode 3 would not be exposed.

As a result of stacking the piezoelectric layers 1, the power supplyelectrodes 2 and the counter electrode 3, each of the piezoelectriclayers 1 is sandwiched by the power supply electrodes 2 (specifically,the first power supply electrode 2A and the second power supplyelectrode 2B) and the counter electrode 3. Thus, when seen in thestacking direction, the power supply electrodes 2 and the counterelectrode 3 are overlapping with each other with the piezoelectric layer1 interposed therebetween. Here, each of the piezoelectric layers 1 ispolarized from the power supply electrode 2 side to the counterelectrode 3 side.

However, the piezoelectric layers 1 include a region in which the powersupply electrodes 2 and the counter electrode 3 are not overlapping whenseen in the stacking direction (see FIG. 12). For example, the firstpower supply lead electrode 2 a, the second power supply lead electrode2 b, and the counter lead electrodes 3 g are not overlapping with thecounter electrode 3 or the power supply electrodes 2 when seen in thestacking direction. In part of the piezoelectric layers 1 correspondingto the non-overlapping region, no electric field occurs. In other words,this part of the piezoelectric layers 1 is piezoelectrically inactive.Specifically, in part of the piezoelectric layers 1 near the short-sidesurfaces, the power supply electrodes 2 and the counter electrode 3 arenot overlapping when seen in the stacking direction. This part of thepiezoelectric layers 1 is piezoelectrically inactive.

The resonance frequency of the stretching vibration and the resonancefrequency of the bending vibration of the piezoelectric element P3,which will be described later, depend on the material, the shape, etc.,of the piezoelectric element P3. The material, the shape, etc., of thepiezoelectric element P3 are determined such that the resonancefrequency of the stretching vibration and the resonance frequency of thebending vibration are approximately equal to each other.

<3.2: Electrical Connection Member>

This embodiment uses the flexible cables F2 of embodiment 2 as theelectrical connection members. FIG. 14 shows the positional relationshipin connection between the first and second flexible cables F21 and F22and the short-side surfaces of the piezoelectric element P3.

The relationship between the first and second flexible cables F21 andF22 and the other elements is the same as that in embodiment 2. Forexample, the relationship between the first flexible cable F21 and thepiezoelectric element P3 is the same as the relationship between thefirst flexible cable F21 and the piezoelectric element P2 in embodiment2. Note that the description of the electrical connection members ofembodiment 3 is provided by applying the description of the <2.2:Electrical Connection Member> section of embodiment 2 of thisspecification mutatis mutandis to this section with “piezoelectricelement P2” being replaced by “piezoelectric element P3” and “FIG. 11”being replaced by “FIG. 14”.

Note that the first and second flexible cables F21 and F22 are notdirectly connected to the first connection external electrode 10A or thesecond connection external electrode 10B.

<3.3: Operation of Ultrasonic Actuator>

Hereinafter, an operation of the ultrasonic actuator is described. Theoperation of the ultrasonic actuator of this embodiment is basically thesame as that of the ultrasonic actuator of embodiment 1. Specifically, afirst driving voltage at a frequency near the substantially-matchedresonance frequencies of the stretching vibration and the bendingvibration of the piezoelectric element P3 is applied to the first powersupply electrode 2A, and a second driving voltage which is approximatelyequal in amplitude and frequency to and different in phase by generally90° or −90° from the first driving voltage is applied to the secondpower supply electrode 2B, whereby the first-order stretching vibrationand the second-order bending vibration are harmonically induced in thepiezoelectric element P3. As a result, the piezoelectric element P3vibrates with its shape being sequentially deformed in the order of FIG.8(A), FIG. 8(B), FIG. 8(C), and FIG. 8(D). The driver elements 8provided on the piezoelectric element P3 make a revolutionary movement,specifically a generally-elliptic movement, when seen in the directionperpendicular to the surface of the sheet of FIG. 8. In other words, thecomposite vibration of the stretching vibration and bending vibration ofthe piezoelectric element P3 causes the driver elements 8 to make anelliptic movement. Due to this elliptic movement, the movable element 9on which the driver elements 8 abut moves relative to the piezoelectricelement P3.

In this example, the first connection external electrode 10A is providedon one of the two long-side surfaces of the piezoelectric element P3,and the second connection external electrode 10B is provided on theother one of the two long-side surfaces. Alternatively, the firstconnection external electrode 10A and the second connection externalelectrode 10B may be provided on the same long-side surface. In thiscase, the first connection external electrode 10A and the secondconnection external electrode 10B may preferably be provided on along-side surface other than the long-side surface provided with thedriver elements 8.

<3.4: Advantages of Embodiment>

According to this embodiment, as in embodiment 2, the first power supplyexternal electrode 4A and the counter external electrodes 5 are providedat different short-side surfaces, and the second power supply externalelectrode 4B and the counter external electrodes 5 are provided atdifferent short-side surfaces. This configuration ensures a sufficientdistance between the first power supply external electrode 4A and thecounter external electrodes 5 and between the second power supplyexternal electrode 4B and the counter external electrodes 5.Accordingly, sufficient insulation can be ensured between the firstpower supply external electrode 4A and the counter external electrodes 5and between the second power supply external electrode 4B and thecounter external electrodes 5.

The first connection external electrode 10A is provided on one of thetwo long-side surfaces of the piezoelectric element P3, and the secondconnection external electrode 10B is provided on the other one of thetwo long-side surfaces. This configuration ensures sufficient insulationbetween the first connection external electrode 10A and the secondconnection external electrode 10B.

Embodiment 3 can also provide effects and advantages substantiallyequivalent to those of embodiments 1 and 2.

<<Embodiment 4 >>

An ultrasonic actuator according to embodiment 4 of the presentinvention is now described. Note that elements equivalent to thosedescribed in the above embodiment are denoted by the same referencecharacters, and the description thereof is herein omitted. Theultrasonic actuator of embodiment 4 is different from embodiment 1 inthe configurations of the piezoelectric element and the flexible cables.

<4.1: Piezoelectric Element P4>

The piezoelectric element P4 of this embodiment is in the shape of agenerally rectangular parallelepiped. The piezoelectric element P4includes a plurality of generally rectangular piezoelectric layers 1,and internal electrode layers interposed between the piezoelectriclayers 1. The piezoelectric element P4 includes the piezoelectric layersand the electrode layers which are stacked in a direction from front toback of the drawing sheet of FIG. 1.

FIG. 15 is an orthographic developed view of the piezoelectric elementP4. FIG. 16 shows the respective layers of the piezoelectric element P4which are seen in the layer stacking direction. In FIG. 15, a portion atthe center represents the principal surface, portions on the right andleft sides of the principal surface are the short-side surfaces, andportions on the upper and lower sides of the principal surface are thelong-side surfaces.

The internal electrode layers are behind the principal surface and thuscannot be seen. The positions of the internal electrode layers projectedover the principal surface are represented by broken lines.

As shown in FIG. 15, power supply external electrodes 4 and counterexternal electrodes 5 are provided on the short-side surfaces of thepiezoelectric element P4. Specifically, the power supply externalelectrodes 4 include a first power supply external electrode 4A and asecond power supply external electrode 4B which are mutually separate.The first power supply external electrode 4A is provided on one of thetwo short-side surfaces of the piezoelectric element P4. The secondpower supply external electrode 4B is provided on the other one of thetwo short-side surfaces of the piezoelectric element P4. Thepiezoelectric element P4 includes the two counter external electrodes 5which are respectively provided on the two short-side surfaces in aone-to-one fashion. Specifically, on one of the short-side surfaces ofthe piezoelectric element P4, the counter external electrode 5 isprovided at one lateral end of the piezoelectric element P4, and thefirst power supply external electrode 4A is provided at the otherlateral end. On the other one of the short-side surfaces of thepiezoelectric element P4, the counter external electrode 5 is providedat one lateral end of the piezoelectric element P4, and the second powersupply external electrode 4B is provided at the other lateral end. Theseelectrodes 4A, 4B and 5 are mutually insulated. In other words, theelectrodes 4A, 4B and 5 are not electrically coupled to one another. Onone of the long-side surfaces of the piezoelectric element P4, a secondconnection external electrode 10B is provided at one longitudinal end ofthe piezoelectric element P4, and a first connection external electrode10A is provided at the other longitudinal end. The first connectionexternal electrode 10A and the second connection external electrode 10Bare mutually insulated.

The power supply electrodes 2 are provided on the principal surface ofat least one of the plurality of piezoelectric layers 1 as shown in FIG.16(B) and FIG. 16(C). Specifically, the power supply electrodes 2 areprovided on the principal surface of at least one of the plurality ofpiezoelectric layers 1 in the first pattern as shown in FIG. 16(B). Onthe principal surface of another one of the plurality of piezoelectriclayers 1 different from the piezoelectric layer 1 on which the powersupply electrodes 2 are provided in the first pattern, the power supplyelectrodes 2 are provided in the second pattern as shown in FIG. 16(C)which is different from the first pattern.

Specifically, the power supply electrodes 2 formed in the first patternand in the second pattern each include first power supply electrodes 2Aand second power supply electrodes 2B which are not electrically coupledto the first power supply electrodes 2A.

In each of the first and second patterns, among four divisional regionsA1-A4 (see FIG. 4) of the principal surface of the piezoelectric layer 1which are defined by halving the principal surface with respect to bothlongitudinal direction L and lateral direction S, the first power supplyelectrodes 2A are provided in two of the four divisional regions A1-A4which are aligned in the first diagonal direction D1 of the principalsurface of the piezoelectric layer 1, i.e., in the divisional regions A2and A4. The second power supply electrodes 2B are provided in the othertwo of the four divisional regions A1-A4 which are aligned in the seconddiagonal direction D2 of the principal surface of the piezoelectriclayer 1, i.e., in the divisional regions A1 and A3.

The first pattern power supply electrodes 2 include a first connectionelectrode J1 extending in the lateral direction at the longitudinalcenter of the principal surface of the piezoelectric layer 1. The firstpower supply electrodes 2A provided in the two divisional regions A2 andA4 of the first pattern are mutually coupled via the first connectionelectrode J1. The second pattern power supply electrodes 2 include asecond connection electrode J2 extending in the lateral direction at thelongitudinal center of the principal surface of the piezoelectric layer1. The second power supply electrodes 2B provided in the two divisionalregions A1 and A3 of the second pattern are mutually coupled via thesecond connection electrode J2.

In each of the first and second patterns, among the first power supplyelectrodes 2A provided in the two divisional regions A2 and A4, thefirst power supply electrode 2A provided in the divisional region A2which is closer to the short-side surface that has the first powersupply external electrode 4A thereon includes a first power supply leadelectrode 2 a extending to the first power supply external electrode 4A.In this way, the first power supply electrode 2A of the divisionalregion A2 is electrically coupled to the first power supply externalelectrode 4A via the first power supply lead electrode 2 a. Among thefirst power supply electrodes 2A provided in the two divisional regionsA2 and A4, the first power supply electrode 2A provided in thedivisional region A4 which is more distant from the short-side surfacethat has the first power supply external electrode 4A thereon includes afirst power supply lead electrode 2 a extending to the first connectionexternal electrode 10A provided on the long-side surface. In this way,the first power supply electrodes 2A of the divisional region A4 in thedifferent piezoelectric layers 1 are electrically coupled to each othervia the first connection external electrode 10A. Since in the firstpattern the first power supply electrode 2A of the divisional region A4is electrically coupled to the first power supply electrode 2A of thedivisional region A2 via the first connection electrode J1, the firstpower supply electrode 2A of the divisional region A4 of the secondpattern, which is electrically coupled to the first power supplyelectrode 2A of the divisional region A4 of the first pattern via thefirst connection external electrode 10A, is electrically coupled to thefirst power supply external electrode 4A of the first pattern via thefirst connection electrode J1.

In each of the first and second patterns, among the second power supplyelectrodes 2B provided in the two divisional regions A1 and A3, thesecond power supply electrode 2B provided in the divisional region A3which is closer to the short-side surface that has the second powersupply external electrode 4B thereon includes a second power supply leadelectrode 2 b extending to the second power supply external electrode4B. In this way, the second power supply electrode 2B of the divisionalregion A3 is electrically coupled to the second power supply externalelectrode 4B via the second power supply lead electrode 2 b. Among thesecond power supply electrodes 2B provided in the two divisional regionsA1 and A3, the second power supply electrode 2B provided in thedivisional region A3 which is more distant from the short-side surfacethat has the second power supply external electrode 4B thereon includesa second power supply lead electrode 2 b extending to the secondconnection external electrode 10B provided on the long-side surface. Inthis way, the second power supply electrodes 2B of the divisional regionA1 in the different piezoelectric layers 1 are electrically coupled toeach other via the second connection external electrode 10B. Since inthe second pattern the second power supply electrode 2B of thedivisional region A1 is electrically coupled to the second power supplyelectrode 2B of the divisional region A3 via the second connectionelectrode J2, the second power supply electrode 2B of the divisionalregion A1 of the first pattern, which is electrically coupled to thesecond power supply electrode 2B of the divisional region A1 of thesecond pattern via the second connection external electrode 10B, iselectrically coupled to the second power supply external electrode 4Bvia the second connection electrode J2 of the second pattern.

The counter electrode 3 is provided over substantially the entiresurface of the piezoelectric layer 1 as shown in FIG. 16(D).Specifically, the counter electrode 3 is not provided in acircumferential region of the principal surface of the piezoelectriclayer 1 but is provided over substantially the entirety of a regioninside the circumferential region. The counter electrode 3 includescounter lead electrodes 3 g which extend from one lateral end to thecounter external electrodes 5 provided on both short-side surfaces ofthe piezoelectric element P4. In this way, the counter electrode 3 iselectrically coupled to the counter external electrodes 5 via thecounter lead electrodes 3 g. The counter electrodes 3 provided ondifferent piezoelectric layers 1 are electrically coupled to each othervia the counter lead electrodes 3 g and the counter external electrodes5.

The piezoelectric element P4 is formed by stacking the piezoelectriclayers 1 provided with the power supply electrodes 2 or the counterelectrode 3 on the principal surfaces as described above. Specifically,the plurality of piezoelectric layers 1 are sequentially stacked in theorder of the piezoelectric layer 1 provided with the first pattern powersupply electrodes 2, the piezoelectric layer 1 provided with the counterelectrode 3, the piezoelectric layer 1 provided with the second patternpower supply electrodes 2, the piezoelectric layer 1 provided with thecounter electrode 3, the piezoelectric layer 1 provided with the firstpattern power supply electrodes 2, the piezoelectric layer 1 providedwith the counter electrode 3, . . . . The piezoelectric layers 1 arestacked such that the principal surfaces provided with the power supplyelectrodes 2 or the counter electrode 3 are oriented in the samedirection, i.e., such that the principal surface of one of thepiezoelectric layers 1 on which the power supply electrodes 2 or thecounter electrode 3 is provided face the principal surface of anotherone of the piezoelectric layers 1 on which none of the power supplyelectrodes 2 and the counter electrode 3 is provided. Note that, thefirst and/or last of the stacked layers are the piezoelectric layers 1which are not provided with the power supply electrodes 2 or the counterelectrode 3 such that the power supply electrodes 2 or the counterelectrode 3 would not be exposed.

As a result of stacking the piezoelectric layers 1, the power supplyelectrodes 2 and the counter electrode 3, each of the piezoelectriclayers 1 is sandwiched by the power supply electrodes 2 (specifically,the first power supply electrode 2A and the second power supplyelectrode 2B) and the counter electrode 3. Thus, when seen in thestacking direction, the power supply electrodes 2 and the counterelectrode 3 are overlapping with each other with the piezoelectric layer1 interposed therebetween. Here, each of the piezoelectric layers 1 ispolarized from the power supply electrode 2 side to the counterelectrode 3 side.

However, the piezoelectric layers 1 include a region in which the powersupply electrodes 2 and the counter electrode 3 are not overlapping whenseen in the stacking direction (see FIG. 15). For example, the firstpower supply lead electrode 2 a, the second power supply lead electrode2 b, and the counter lead electrodes 3 g are not overlapping with thecounter electrode 3 or the power supply electrodes 2 when seen in thestacking direction. In part of the piezoelectric layers 1 correspondingto the non-overlapping region, no electric field occurs. In other words,this part of the piezoelectric layers 1 is piezoelectrically inactive.Specifically, in part of the piezoelectric layers 1 near the short-sidesurfaces, the power supply electrodes 2 and the counter electrode 3 arenot overlapping when seen in the stacking direction. This part of thepiezoelectric layers 1 is piezoelectrically inactive.

The resonance frequency of the stretching vibration and the resonancefrequency of the bending vibration of the piezoelectric element P4,which will be described later, depend on the material, the shape, etc.,of the piezoelectric element P4. The material, the shape, etc., of thepiezoelectric element P4 are determined such that the resonancefrequency of the stretching vibration and the resonance frequency of thebending vibration are approximately equal to each other.

<4.2: Electrical Connection Member>

In this embodiment, flexible cables F4 are used as the electricalconnection member. The flexible cables F4 include a first flexible cableF41 and a second flexible cable F42. As shown in FIG. 1, the firstflexible cable F41 and the second flexible cable F42 are electricallyconnected to the respective short-side surfaces of the piezoelectricelement P4. The first flexible cable F41 and the second flexible cableF42 are electrically coupled to the piezoelectric element P4. The firstflexible cable F41 and the second flexible cable F42 have substantiallythe same shape.

FIG. 17 shows the positional relationship in connection between thefirst and second flexible cables F41 and F42 and the short-side surfacesof the piezoelectric element P4. As shown in FIG. 17, the first andsecond flexible cables F41 and F42 include a plurality of electric wiresformed by printing copper over an insulative resin substrate. Theelectric wires are mutually insulated.

The first flexible cable F41 is connected to one of the short-sidesurfaces of the piezoelectric element P4. The second flexible cable F42is connected to the other one of the short-side surfaces of thepiezoelectric element P4. The first and second flexible cables F41 andF42 each include an electric line 6 connected to the power supplyexternal electrode 4 and an electric line 7 connected to the counterexternal electrode 5. Specifically, the first flexible cable F41 has anelectric line 6A connected to the first power supply external electrode4A and an electric line 7 connected to the counter external electrode 5.The second flexible cable F42 has an electric line 6B connected to thesecond power supply external electrode 4B and an electric line 7connected to the counter external electrode 5.

Note that the flexible cables F4 are not directly connected to the firstconnection external electrode 10A or the second connection externalelectrode 10B.

The first flexible cable F41 has a shape symmetrical about a plane whichpasses through the midpoints of the short sides of the principal planeof the piezoelectric layer 1 and which is perpendicular to theshort-side surfaces. The second flexible cable F42 also has a shapesymmetrical about the plane which passes through the midpoints of theshort sides of the principal plane of the piezoelectric layer 1 andwhich is perpendicular to the short-side surfaces. The first flexiblecable F41 and the second flexible cable F42 have a shape symmetricalabout a plane which passes through the midpoints of the long sides ofthe principal plane of the piezoelectric layer 1 and which isperpendicular to the principal surface. A connecting portion of thefirst flexible cable F41 which is connected to the piezoelectric elementP4 has a shape symmetrical about the plane which passes through themidpoints of the short sides of the principal plane of the piezoelectriclayer 1 and which is perpendicular to the short-side surfaces. Aconnecting portion of the second flexible cable F42 which is connectedto the piezoelectric element P4 also has a shape symmetrical about theplane which passes through the midpoints of the short sides of theprincipal plane of the piezoelectric layer 1 and which is perpendicularto the short-side surfaces. The connecting portion of the first flexiblecable F41 which is connected to the piezoelectric element P4 and theconnecting portion of the second flexible cable F42 which is connectedto the piezoelectric element P4 have a shape symmetrical about the planewhich passes through the midpoints of the long sides of the principalplane of the piezoelectric layer 1 and which is perpendicular to theprincipal surface.

In the connecting portions of the first and second flexible cables F41and F42 and a connecting portion of the piezoelectric element P4, theseelements are electrically connected and adhered using an anisotropicconductive adhesion sheet. The anisotropic conductive adhesion sheet isprepared by molding a resin containing electrically conductive particlesdispersed therein into the form of a sheet. The anisotropic conductiveadhesion sheet has an electric conductivity in the adhesion direction,i.e., in the sheet thickness direction, but lacks electric conductivityin the in-plane directions of the adhesion surface. Therefore, theplurality of electrodes provided over the short-side surfaces of thepiezoelectric element P4 can be electrically connected to the respectiveelectric lines of the first and second flexible cables F41 and F42 by asingle anisotropic conductive adhesion sheet with the electrodes beingmutually insulated. In the first step of the connection method, ananisotropic conductive sheet is sandwiched between the first and secondflexible cables F41 and F42 made of polyimide and the piezoelectricelement P4. Then, the first and second flexible cables F41 and F42 arepressed against the piezoelectric element P4 using a heated planarcautery. As a result, the first and second flexible cables F41 and F42and the piezoelectric element P4 are electrically coupled by theelectrically conductive particles and adhered by means of the resin ofthe anisotropic conductive adhesion sheet.

The connection portions of the first and second flexible cables F41 andF42 and the piezoelectric element P4 are respectively interposed betweenthe supporting portion 13 a and the piezoelectric element P4 and betweenthe supporting portion 13 c and the piezoelectric element P4.Specifically, the first flexible cable F41 is pressed by the supportingportion 13 a against the piezoelectric element P4. The second flexiblecable F42 is pressed by the supporting portion 13 c against thepiezoelectric element P4.

The electric lines 6 connected to the power supply external electrodes 4are an example of the power supply conductive member. The electric line6A connected to the first power supply external electrode 4A is anexample of the first power supply conductive member. The electric line6B connected to the second power supply external electrode 4B is anexample of the second power supply conductive member. The electric lines7 connected to the counter external electrodes 5 are an example of thecounter conductive member. The first flexible cable F41 is an example ofthe first electrical connection member. The second flexible cable F42 isan example of the second electrical connection member.

The first and second flexible cables F41 and F42 are coupled to a powersupply (not shown). A driving voltage from the power supply is appliedto the piezoelectric element P4 via the first and second flexible cablesF41 and F42 such that vibration is generated in the piezoelectricelement P4.

<4.3: Operation of Ultrasonic Actuator>

Hereinafter, an operation of the ultrasonic actuator is described. Theoperation of the ultrasonic actuator of this embodiment is basically thesame as that of the ultrasonic actuator of embodiment 1. Specifically, afirst driving voltage at a frequency near the substantially-matchedresonance frequencies of the stretching vibration and the bendingvibration of the piezoelectric element P4 is applied to the first powersupply electrode 2A, and a second driving voltage which is approximatelyequal in amplitude and frequency to and different in phase by generally90° or −90° from the first driving voltage is applied to the secondpower supply electrode 2B, whereby the first-order stretching vibrationand the second-order bending vibration are harmonically induced in thepiezoelectric element P4. As a result, the piezoelectric element P4vibrates with its shape being sequentially deformed in the order of FIG.8(A), FIG. 8(B), FIG. 8(C), and FIG. 8(D). The driver elements 8provided on the piezoelectric element P4 make a revolutionary movement,specifically a generally-elliptic movement, when seen in the directionperpendicular to the surface of the sheet of FIG. 8. In other words, thecomposite vibration of the stretching vibration and bending vibration ofthe piezoelectric element P4 causes the driver elements 8 to make anelliptic movement. Due to this elliptic movement, the movable element 9on which the driver elements 8 abut moves relative to the piezoelectricelement P4.

In this example, the first connection external electrode 10A and thesecond connection external electrode 10B are provided on the samelong-side surface. Alternatively, the first and second connectionexternal electrodes 10A and 10B may be provided on different long-sidesurfaces of the piezoelectric element P4.

<4.4: Advantages of Embodiment>

According to this embodiment, the first connection external electrode10A and the second connection external electrode 10B are provided on thesame long-side surface. Specifically, the long-side surface which hasthe driving elements 8 is not provided with the first connectionexternal electrode 10A or the second connection external electrode 10B,and the other long-side surface which is different from the long-sidesurface that has the driving elements 8 thereon is provided with thefirst connection external electrode 10A and the second connectionexternal electrode 10B. This configuration improves the flexibility ofarrangement of the driving elements 8 such that the driving elements 8are fixed at positions other than the first connection externalelectrode 10A or the second connection external electrode 10B.

Embodiment 4 can also provide effects and advantages substantiallyequivalent to those of embodiments 1 and 2.

<<Embodiment 5 >>

An ultrasonic actuator according to embodiment 5 of the presentinvention is now described. Note that elements equivalent to thosedescribed in the above embodiment are denoted by the same referencecharacters, and the description thereof is herein omitted. Theultrasonic actuator of embodiment 5 is different from embodiment 1 inthe configurations of the piezoelectric element and the flexible cables.

<5.1: Piezoelectric Element P5>

The piezoelectric element P5 of this embodiment is in the shape of agenerally rectangular parallelepiped. The piezoelectric element P5includes a plurality of generally rectangular piezoelectric layers 1,and internal electrode layers interposed between the piezoelectriclayers 1. The piezoelectric element P5 includes the piezoelectric layersand the electrode layers which are stacked in a direction from front toback of the drawing sheet of FIG. 1.

FIG. 18 is an orthographic developed view of the piezoelectric elementP5. FIG. 19 shows the respective layers of the piezoelectric element P5which are seen in the layer stacking direction. In FIG. 18, a portion atthe center represents the principal surface, portions on the right andleft sides of the principal surface are the short-side surfaces, andportions on the upper and lower sides of the principal surface are thelong-side surfaces. The internal electrode layers are behind theprincipal surface and thus cannot be seen. The positions of the internalelectrode layers projected over the principal surface are represented bybroken lines.

As shown in FIG. 18, power supply external electrodes 4 and counterexternal electrodes 5 are provided on the short-side surfaces of thepiezoelectric element P5. Specifically, the power supply externalelectrodes 4 include a first power supply external electrode 4A and asecond power supply external electrode 4B which are mutually separate.The first power supply external electrode 4A and the second power supplyexternal electrode 4B are provided on one of the two short-side surfacesof the piezoelectric element P5. The counter external electrodes 5include a first counter external electrode 5A and a second counterexternal electrode 5B. The first counter external electrode 5A and thesecond counter external electrode 5B are provided on the other one ofthe two short-side surfaces of the piezoelectric element P5. Thepiezoelectric element P5 includes the two counter external electrodes 5which are provided on the other one of the two short-side surfaces.These electrodes 4A, 4B, 5A, and 5B are mutually insulated. In otherwords, the electrodes 4A, 4B, 5A, and 5B are not electrically coupled toone another. A first connection external electrode 10A and a fourthconnection external electrode 10D are provided on one of the long-sidesurfaces of the piezoelectric element P5. A second connection externalelectrode 10B and a third connection external electrode 10C are providedon the other one of the long-side surfaces of the piezoelectric elementP5. The first through fourth connection external electrodes 10A-10D aremutually insulated. In other words, the first through fourth connectionexternal electrodes 10A-10D are not electrically coupled to one another.The power supply electrodes 2 are provided on the principal surface ofat least one of the plurality of piezoelectric layers 1 as shown in FIG.19(B) and FIG. 19(C). Specifically, the power supply electrodes 2 areprovided on the principal surface of at least one of the plurality ofpiezoelectric layers 1 in the first pattern as shown in FIG. 19(B). Onthe principal surface of another one of the plurality of piezoelectriclayers 1 different from the piezoelectric layer 1 on which the powersupply electrodes 2 are provided in the first pattern, the power supplyelectrodes 2 are provided in the second pattern as shown in FIG. 19(C)which is different from the first pattern.

Specifically, the power supply electrodes 2 formed in the first patternand in the second pattern each include first power supply electrodes 2Aand second power supply electrodes 2B which are not electrically coupledto the first power supply electrodes 2A.

In each of the first and second patterns, among four divisional regionsA1-A4 (see FIG. 4) of the principal surface of the piezoelectric layer 1which are defined by halving the principal surface with respect to bothlongitudinal direction L and lateral direction S, the first power supplyelectrodes 2A are provided in two of the four divisional regions A1-A4which are aligned in the first diagonal direction D1 of the principalsurface of the piezoelectric layer 1, i.e., in the divisional regions A2and A4. The second power supply electrodes 2B are provided in the othertwo of the four divisional regions A1-A4 which are aligned in the seconddiagonal direction D2 of the principal surface of the piezoelectriclayer 1, i.e., in the divisional regions A1 and A3.

The first pattern power supply electrodes 2 include a first connectionelectrode J1 extending in the lateral direction at the longitudinalcenter of the principal surface of the piezoelectric layer 1. The firstpower supply electrodes 2A provided in the two divisional regions A2 andA4 of the first pattern are mutually coupled via the first connectionelectrode J1. On the other hand, the second pattern power supplyelectrodes 2 include a second connection electrode J2 extending in thelateral direction at the longitudinal center of the principal surface ofthe piezoelectric layer 1. The second power supply electrodes 2Bprovided in the two divisional regions A1 and A3 of the second patternare mutually coupled via the second connection electrode J2.

In each of the first and second patterns, among the first power supplyelectrodes 2A provided in the two divisional regions A2 and A4, thefirst power supply electrode 2A provided in the divisional region A2which is closer to the short-side surface that has the first powersupply external electrode 4A thereon includes a first power supply leadelectrode 2 a extending to the first power supply external electrode 4A.In this way, the first power supply electrode 2A of the divisionalregion A2 is electrically coupled to the first power supply externalelectrode 4A via the first power supply lead electrode 2 a. Among thefirst power supply electrodes 2A provided in the two divisional regionsA2 and A4, the first power supply electrode 2A provided in thedivisional region A4 which is more distant from the short-side surfacethat has the first power supply external electrode 4A thereon includes afirst power supply lead electrode 2 a extending to the first connectionexternal electrode 10A provided on the long-side surface. In this way,the first power supply electrodes 2A of the divisional region A4 in thedifferent piezoelectric layers 1 are electrically coupled to each othervia the first connection external electrode 10A. Since in the firstpattern the first power supply electrode 2A of the divisional region A4is electrically coupled to the first power supply electrode 2A of thedivisional region A2 via the first connection electrode J1, the firstpower supply electrode 2A of the divisional region A4 of the secondpattern, which is electrically coupled to the first power supplyelectrode 2A of the divisional region A4 of the first pattern via thefirst connection external electrode 10A, is electrically coupled to thefirst power supply external electrode 4A of the first pattern via thefirst connection electrode J1.

In each of the first and second patterns, among the second power supplyelectrodes 2B provided in the two divisional regions A1 and A3, thesecond power supply electrode 2B provided in the divisional region A3which is closer to the short-side surface that has the second powersupply external electrode 4B thereon includes a second power supply leadelectrode 2 b extending to the second power supply external electrode4B. In this way, the second power supply electrode 2B of the divisionalregion A3 is electrically coupled to the second power supply externalelectrode 4B via the second power supply lead electrode 2 b. Among thesecond power supply electrodes 2B provided in the two divisional regionsA1 and A3, the second power supply electrode 2B provided in thedivisional region A1 which is more distant from the short-side surfacethat has the second power supply external electrode 4B thereon includesa second power supply lead electrode 2 b extending to the secondconnection external electrode 10B provided on the long-side surface. Inthis way, the second power supply electrodes 2B of the divisional regionA1 in the different piezoelectric layers 1 are electrically coupled toeach other via the second connection external electrode 10B. Since inthe second pattern the second power supply electrode 2B of thedivisional region A1 is electrically coupled to the second power supplyelectrode 2B of the divisional region A3 via the second connectionelectrode J2, the second power supply electrode 2B of the divisionalregion A1 of the first pattern, which is electrically coupled to thesecond power supply electrode 2B of the divisional region A1 of thesecond pattern via the second connection external electrode 10B, iselectrically coupled to the second power supply external electrode 4Bvia the second connection electrode J2 of the second pattern.

The counter electrodes 3 are provided on the principal surface of atleast one of the plurality of piezoelectric layers 1 on which the powersupply electrodes 2 are not provided as shown in FIG. 19(D) and FIG.19(E). Specifically, the counter electrodes 3 are provided in the thirdpattern on the principal surface of at least one of the plurality ofpiezoelectric layers 1 on which the power supply electrodes 2 are notprovided as shown in FIG. 19(D). On the principal surface of another oneof the plurality of piezoelectric layers 1 on which none of the powersupply electrodes 2 and the third pattern counter electrodes 3 areprovided, counter electrodes 3 are provided in the fourth pattern asshown in FIG. 19(E) which is different from the third pattern.

Specifically, the counter electrodes 3 formed in the third pattern andin the fourth pattern each include first counter electrodes 3A andsecond counter electrodes 3B which are not electrically coupled to thefirst counter electrodes 3A.

In each of the third and fourth patterns, among four divisional regionsA1-A4 (see FIG. 4) of the principal surface of the piezoelectric layer 1which are defined by halving the principal surface with respect to bothlongitudinal direction L and lateral direction S, the first counterelectrodes 3A are provided in two of the four divisional regions A1-A4which are aligned in the first diagonal direction D1 of the principalsurface of the piezoelectric layer 1, i.e., in the divisional regions A2and A4. The second counter electrodes 3B are provided in the other twoof the four divisional regions A1-A4 which are aligned in the seconddiagonal direction D2 of the principal surface of the piezoelectriclayer 1, i.e., in the divisional regions A1 and A3.

The third pattern counter electrodes 3 include a third connectionelectrode J3 extending in the lateral direction at the longitudinalcenter of the principal surface of the piezoelectric layer 1. The firstcounter electrodes 3A provided in the two divisional regions A2 and A4of the third pattern are electrically coupled to each other via thethird connection electrode J3. On the other hand, the fourth patterncounter electrodes 3 include a fourth connection electrode J4 extendingin the lateral direction at the longitudinal center of the principalsurface of the piezoelectric layer 1. The second counter electrodes 3Bprovided in the two divisional regions A1 and A3 of the fourth patternare electrically coupled to each other via the fourth connectionelectrode J4.

In each of the third and fourth patterns, among the first counterelectrodes 3A provided in the two divisional regions A2 and A4, thefirst counter electrodes 3A provided in the divisional region A4 whichis closer to the short-side surface that has the first counter externalelectrode 5A thereon includes a first counter lead electrode 3 aextending to the first counter external electrode 5A. In this way, thefirst counter electrode 3A of the divisional region A4 is electricallycoupled to the first counter external electrode 5A via the first counterlead electrode 3 a. Among the first counter electrodes 3A provided inthe two divisional regions A2 and A4, the first counter electrode 3Aprovided in the divisional region A2 which is more distant from theshort-side surface that has the first counter external electrode 5Athereon includes a first counter lead electrode 3 a extending to thethird connection external electrode 10C provided on the long-sidesurface. In this way, the first counter electrodes 3A of the divisionalregion A2 in the different piezoelectric layers 1 are electricallycoupled to each other via the third connection external electrode 10C.Since in the third pattern the first counter electrode 3A of thedivisional region A2 is electrically coupled to the first counterelectrode 3A of the divisional region A4 via the third connectionelectrode J3, the first counter electrode 3A of the divisional region A2of the fourth pattern, which is electrically coupled to the firstcounter electrode 3A of the divisional region A2 of the third patternvia the third connection external electrode 10C, is electrically coupledto the first counter external electrode 5A via the third connectionelectrode J3 of the third pattern.

In each of the third and fourth patterns, among the second counterelectrodes 3B provided in the two divisional regions A1 and A3, thesecond counter electrode 3B provided in the divisional region A1 whichis closer to the short-side surface that has the second counter externalelectrode 5B thereon includes a second counter lead electrode 3 bextending to the second counter external electrode 5B. In this way, thesecond counter electrodes 3B of the divisional region A1 is electricallycoupled to the second counter external electrode 5B via the secondcounter lead electrode 3 b. Among the second counter electrodes 3Bprovided in the two divisional regions A1 and A3, the second counterelectrode 3B provided in the divisional region A3 which is more distantfrom the short-side surface that has the second counter externalelectrode 5B thereon includes a second counter lead electrode 3 bextending to the fourth connection external electrode 10D provided onthe long-side surface. In this way, the second counter electrodes 3B ofthe divisional region A3 in the different piezoelectric layers 1 areelectrically coupled to each other via the second connection externalelectrode 10B. Since in the fourth pattern the second counter electrode3B of the divisional region A3 is electrically coupled to the secondcounter electrode 3B of the divisional region A1 via the fourthconnection electrode J4, the second counter electrodes 3B of thedivisional region A3 of the third pattern, which is electrically coupledto the second counter electrode 3B of the divisional region A3 of thefourth pattern via the fourth connection external electrode 10D, iselectrically coupled to the second counter external electrode 5B via thefourth connection electrode J4 of the fourth pattern.

The piezoelectric element P5 is formed by stacking the piezoelectriclayers 1 provided with the power supply electrodes 2 or the counterelectrodes 3 on the principal surfaces as described above. Specifically,the plurality of piezoelectric layers 1 are sequentially stacked in theorder of the piezoelectric layer 1 provided with the first pattern powersupply electrodes 2, the piezoelectric layer 1 provided with the thirdpattern counter electrodes 3, the piezoelectric layer 1 provided withthe second pattern power supply electrodes 2, the piezoelectric layer 1provided with the fourth pattern counter electrodes 3, the piezoelectriclayer 1 provided with the first pattern power supply electrodes 2, thepiezoelectric layer 1 provided with the third pattern counter electrodes3, . . . . The piezoelectric layers 1 are stacked such that theprincipal surfaces provided with the power supply electrodes 2 or thecounter electrodes 3 are oriented in the same direction, i.e., such thatthe principal surface of one of the piezoelectric layers 1 on which thepower supply electrodes 2 or the counter electrodes 3 are provided facethe principal surface of another one of the piezoelectric layers 1 onwhich none of the power supply electrodes 2 and the counter electrodes 3is provided. Note that, the first and/or last of the stacked layers arethe piezoelectric layers 1 which are not provided with the power supplyelectrodes 2 or the counter electrodes 3 such that the power supplyelectrodes 2 or the counter electrodes 3 would not be exposed.

As a result of stacking the piezoelectric layers 1, the power supplyelectrodes 2 and the counter electrodes 3, each of the piezoelectriclayers 1 is sandwiched by the power supply electrodes 2 and the counterelectrodes 3. Thus, when seen in the stacking direction, the powersupply electrodes 2 and the counter electrodes 3 are overlapping witheach other with the piezoelectric layer 1 interposed therebetween. Here,each of the piezoelectric layers 1 is polarized from the power supplyelectrode 2 side to the counter electrode 3 side.

Specifically, the first power supply electrodes 2A are overlapping withthe first counter electrodes 3A with the piezoelectric layer 1interposed therebetween when seen in the stacking direction. The secondpower supply electrodes 2B are overlapping with the second counterelectrodes 3B with the piezoelectric layer 1 interposed therebetweenwhen seen in the stacking direction. The first connection electrode J1is overlapping with the third connection electrode J3 with thepiezoelectric layer 1 interposed therebetween when seen in the stackingdirection. The second connection electrode J2 is overlapping with thefourth connection electrode J4 with the piezoelectric layer 1 interposedtherebetween when seen in the stacking direction.

However, the piezoelectric layers 1 include a region in which the powersupply electrodes 2 and the counter electrodes 3 are not overlappingwhen seen in the stacking direction (see FIG. 18). For example, thefirst and second power supply lead electrodes 2 a and 2 b and thecounter lead electrodes 3 a and 3 b are not overlapping with the counterelectrodes 3 or the power supply electrodes 2 when seen in the stackingdirection. In part of the piezoelectric layers 1 corresponding to thenon-overlapping region, no electric field occurs. In other words, thispart of the piezoelectric layers 1 is piezoelectrically inactive.Specifically, in part of the piezoelectric layers 1 near the short-sidesurfaces, the power supply electrodes 2 and the counter electrodes 3 arenot overlapping when seen in the stacking direction. This part of thepiezoelectric layers 1 is piezoelectrically inactive.

The resonance frequency of the stretching vibration and the resonancefrequency of the bending vibration of the piezoelectric element P5,which will be described later, depend on the material, the shape, etc.,of the piezoelectric element P5. The material, the shape, etc., of thepiezoelectric element P5 are determined such that the resonancefrequency of the stretching vibration and the resonance frequency of thebending vibration are approximately equal to each other.

<5.2: Electrical Connection Member>

In this embodiment, flexible cables F5 are used as the electricalconnection member. The flexible cables F5 include a first flexible cableF51 and a second flexible cable F52. As shown in FIG. 1, the firstflexible cable F51 and the second flexible cable F52 are electricallyconnected to the respective short-side surfaces of the piezoelectricelement P5. The first flexible cable F51 and the second flexible cableF52 are electrically connected to the piezoelectric element P5. Thefirst flexible cable F51 and the second flexible cable F52 havesubstantially the same shape.

FIG. 20 shows the positional relationship in connection between thefirst and second flexible cables F51 and F52 and the lateral surfaces ofthe piezoelectric element P5. As shown in FIG. 20, the first and secondflexible cables F51 and F52 include a plurality of electric wires formedby printing copper over an insulative resin substrate. The electricwires are mutually insulated.

The first flexible cable F51 is connected to one of the short-sidesurfaces of the piezoelectric element P5. The first flexible cable F51includes electric lines 6 connected to the power supply externalelectrodes 4. Specifically, the first flexible cable F51 has an electricline 6A connected to the first power supply external electrode 4A and anelectric line 6B connected to the second power supply external electrode4B.

The second flexible cable F52 is connected to the other one of theshort-side surfaces of the piezoelectric element P5. The second flexiblecable F52 includes electric lines 7 connected to the counter externalelectrodes 5. Specifically, the second flexible cable F52 has anelectric line 7A connected to the first counter external electrode 5Aand an electric line 7B connected to the second counter externalelectrode 5B. The electric line 7A constitutes the first counterconductive member, and the electric line 7B constitutes the secondcounter conductive member.

Note that the flexible cables F5 are not directly connected to the firstthrough fourth connection external electrodes 10A-10D.

The first flexible cable F51 has a shape symmetrical about a plane whichpasses through the midpoints of the short sides of the principal planeof the piezoelectric layer 1 and which is perpendicular to theshort-side surfaces. The second flexible cable F52 also has a shapesymmetrical about the plane which passes through the midpoints of theshort sides of the principal plane of the piezoelectric layer 1 andwhich is perpendicular to the short-side surfaces. The first flexiblecable F51 and the second flexible cable F52 have a shape symmetricalabout a plane which passes through the midpoints of the long sides ofthe principal plane of the piezoelectric layer 1 and which isperpendicular to the principal surface. A connecting portion of thefirst flexible cable F51 which is connected to the piezoelectric elementP5 has a shape symmetrical about the plane which passes through themidpoints of the short sides of the principal plane of the piezoelectriclayer 1 and which is perpendicular to the short-side surfaces. Aconnecting portion of the second flexible cable F52 which is connectedto the piezoelectric element P5 also has a shape symmetrical about theplane which passes through the midpoints of the short sides of theprincipal plane of the piezoelectric layer 1 and which is perpendicularto the short-side surfaces. The connecting portion of the first flexiblecable F51 which is connected to the piezoelectric element P5 and theconnecting portion of the second flexible cable F52 which is connectedto the piezoelectric element P5 have a shape symmetrical about the planewhich passes through the midpoints of the long sides of the principalplane of the piezoelectric layer 1 and which is perpendicular to theprincipal surface.

In the connecting portions of the first and second flexible cables F51and F52 and a connecting portion of the piezoelectric element P5, theseelements are electrically connected and adhered using an anisotropicconductive adhesion sheet. The anisotropic conductive adhesion sheet isprepared by molding a resin containing electrically conductive particlesdispersed therein into the form of a sheet. The anisotropic conductiveadhesion sheet has an electric conductivity in the adhesion direction,i.e., in the sheet thickness direction, but lacks electric conductivityin the in-plane directions of the adhesion surface. Therefore, theplurality of electrodes provided over the short-side surfaces of thepiezoelectric element P5 can be electrically connected to the respectiveelectric lines of the first and second flexible cables F51 and F52 by asingle anisotropic conductive adhesion sheet with the electrodes beingmutually insulated. In the first step of the connection method, ananisotropic conductive sheet is sandwiched between the first and secondflexible cables F51 and F52 made of polyimide and the piezoelectricelement P5. Then, the first and second flexible cables F51 and F52 arepressed against the piezoelectric element P5 using a heated planarcautery. As a result, the first and second flexible cables F51 and F52and the piezoelectric element P5 are electrically coupled by theelectrically conductive particles and adhered by means of the resin ofthe anisotropic conductive adhesion sheet.

The connection portions of the first and second flexible cables F51 andF52 and the piezoelectric element P5 are respectively interposed betweenthe supporting portion 13 a and the piezoelectric element P5 and betweenthe supporting portion 13 c and the piezoelectric element P5.Specifically, the first flexible cable F51 is pressed by the supportingportion 13 a against the piezoelectric element P5. The second flexiblecable F52 is pressed by the supporting portion 13 c against thepiezoelectric element P5.

The electric lines 6 connected to the power supply external electrodes 4are an example of the power supply conductive member. The electric line6A connected to the first power supply external electrode 4A is anexample of the first power supply conductive member. The electric line6B connected to the second power supply external electrode 4B is anexample of the second power supply conductive member. The electric lines7 connected to the counter external electrodes 5 are an example of thecounter conductive member. The electric line 7A connected to the firstcounter external electrode 5A is an example of the first power supplyconductive member. The electric line 7B connected to the second counterexternal electrode 5B is an example of the second counter conductivemember. The first flexible cable F51 is an example of the firstelectrical connection member. The second flexible cable F52 is anexample of the second electrical connection member.

The first and second flexible cables F51 and F52 are coupled to a powersupply (not shown). A driving voltage from the power supply is appliedto the piezoelectric element P5 via the first and second flexible cablesF51 and F52 such that vibration is generated in the piezoelectricelement P5.

<5.3: Operation of Ultrasonic Actuator>

Hereinafter, an operation of the ultrasonic actuator is described.

A first driving voltage at a frequency near the substantially-matchedresonance frequencies of the stretching vibration and the bendingvibration of the piezoelectric element P5 is applied between the firstpower supply electrode 2A and the first counter electrode 3A, and asecond driving voltage which is approximately equal in amplitude andfrequency to and different in phase by generally 90° or −90° from thefirst driving voltage is applied between the second power supplyelectrode 2B and the second counter electrode 3B, whereby the first modestretching vibration and the second mode bending vibration areharmonically induced in the piezoelectric element P5. As a result, thepiezoelectric element P5 vibrates with its shape being sequentiallydeformed in the order of FIG. 8(A), FIG. 8(B), FIG. 8(C), and FIG. 8(D).The driver elements 8 provided on the piezoelectric element P5 make arevolutionary movement, specifically a generally-elliptic movement, whenseen in the direction perpendicular to the surface of the sheet of FIG.8. In other words, the composite vibration of the stretching vibrationand bending vibration of the piezoelectric element P5 causes the driverelements 8 to make an elliptic movement. Due to this elliptic movement,the movable element 9 on which the driver elements 8 abut moves relativeto the piezoelectric element P5.

In this embodiment, the power supply applies to the first counterelectrode 3A a voltage opposite in polarity to that applied to the firstpower supply electrode 2A. The power supply applies to the secondcounter electrode 3B a voltage opposite in polarity to that applied tothe second power supply electrode 2B. This power supply may beimplemented using a full-bridge circuit, a push-pull circuit, or thelike. This structure is possible because the counter electrodes 3include the first counter electrodes 3A and the second counterelectrodes 3B which are separate from each other.

Although the first power supply external electrode 4A and the secondpower supply external electrode 4B are provided on one of the twoshort-side surfaces of the piezoelectric element P5 while the firstcounter external electrode 5A and the second counter external electrode5B are provided on the other one of the two short-side surfaces, anycombination of these electrodes may be possible. The structure in whichthe first power supply external electrode 4A is provided on one of thetwo short-side surfaces of the piezoelectric element P5 while the firstcounter external electrode 5A is provided on the other one of the twoshort-side surfaces and in which the second power supply externalelectrode 4B is provided on one of the two short-side surfaces of thepiezoelectric element P5 while the second counter external electrode 5Bis provided on the other one of the two short-side surfaces may beimplemented by an alternative structure in which both the first powersupply external electrode 4A and the second counter external electrode5B are provided on one of the two short-side surfaces of thepiezoelectric element P5 while both the first counter external electrode5A and the second power supply external electrode 4B are provided on theother one of the two short-side surfaces.

Both the first counter electrodes 3A and the second counter electrodes3B may be coupled to the ground.

Although the above-described example uses one piece of the piezoelectricelement P5 which is coupled to the power supply, two or more pieces ofthe piezoelectric elements P5 may be used and may be connected in seriesand coupled to the power supply. In this case, for example, the serialconnection may be implemented by electrically coupling the secondcounter external electrode 5B of the first piezoelectric element P5 tothe second power supply external electrode 4B of the secondpiezoelectric element P5 using an electrical connection member, such asa flexible, or the like, and electrically coupling the first counterexternal electrode 5A of the first piezoelectric element P5 to the firstpower supply external electrodes 4A of the second piezoelectric elementP5 using an electrical connection member, such as a flexible, or thelike.

<5.4: Advantages of Embodiment>

According to this embodiment, as in embodiment 2, the first power supplyexternal electrode 4A and the counter external electrodes 5 are providedat different short-side surfaces of the piezoelectric element P5, andthe second power supply external electrode 4B and the counter externalelectrodes 5 are provided at different short-side surfaces. Thisconfiguration ensures a sufficient distance between the first powersupply external electrode 4A and the counter external electrodes 5 andbetween the second power supply external electrode 4B and the counterexternal electrodes 5. Accordingly, sufficient insulation can be ensuredbetween the first power supply external electrode 4A and the counterexternal electrodes 5 and between the second power supply externalelectrode 4B and the counter external electrodes 5.

Since the counter electrodes 3 include the first counter electrodes 3Aand the second counter electrodes 3B which are separate from each other,a voltage opposite in polarity to that applied to the first power supplyelectrodes 2A can be applied to the first counter electrodes 3A, and avoltage opposite in polarity to that applied to the second power supplyelectrodes 2B can be applied to the second counter electrodes 3B.Therefore, the voltage applied to the piezoelectric layer 1 can be twicethat applied when the counter electrodes 3 are coupled to the ground.Further, due to this configuration, a plurality of pieces of thepiezoelectric elements P5 can be connected in series as described above.

The first power supply external electrode 4A is provided on one of thetwo short-side surfaces of the piezoelectric element, and the firstcounter external electrode 5A is provided on the other one of the twoshort-side surfaces which is different from that on which the firstpower supply external electrode 4A is provided. This configurationensures a large distance between the first power supply externalelectrode 4A and the first counter external electrode 5A. Thisconfiguration also improves insulation between the first power supplyexternal electrode 4A and the first counter external electrode 5A.Likewise, the second power supply external electrode 4B is provided onone of the two short-side surfaces of the piezoelectric element, and thesecond counter external electrode 5B is provided on the other one of thetwo short-side surfaces which is different from that on which the secondpower supply external electrode 4B is provided. This configurationensures a large distance between the second power supply externalelectrode 4B and the second counter external electrode 5B. Thisconfiguration also improves insulation between the second power supplyexternal electrode 4B and the second counter external electrode 5B.

The principal surface of the piezoelectric layer 1 on which the firstcounter electrodes 3A are provided has the third connection electrode J3which provides electrical connection between the first counterelectrodes 3A. The principal surface of another piezoelectric layer 1,which is different from the principal surface that has the thirdconnection electrode J3 thereon, has the fourth connection electrode J4which provides electrical connection between the second counterelectrodes 3B. This configuration enables reduction of the number of thefirst counter external electrodes 5A which are electrically coupled tothe first counter electrodes 3A and the number of the second counterexternal electrodes 5B which are electrically coupled to the secondcounter electrodes 3B. As a result, the number of connection pointsbetween the piezoelectric element P5 and the electrical connectionmembers can be reduced, and accordingly, the probability of occurrenceof peeling at the connection faces between the piezoelectric element P5and the electrical connection members. Further, the factors ofinterference with the vibration of the piezoelectric element P5 aredecreased so that the efficiency of the vibration can be improved.

The third and fourth connection electrodes J3 and J4 have a shapeelongated in the lateral direction at the longitudinal center of theprincipal surface of the piezoelectric layer 1. Therefore, the counterelectrodes 3 can have an increased area at the longitudinal center ofthe piezoelectric layer 1. By increasing the areas of the third andfourth connection electrodes J3 and J4, large stretching vibration canbe induced even when the size of the piezoelectric element P5 isreduced. As a result, the efficiency of the ultrasonic actuator can beimproved.

Embodiment 5 can also provide effects and advantages substantiallyequivalent to those of embodiments 1 and 2.

<<Other Embodiments>>

According to the present invention, the above-described embodiments mayhave different structures which are described below.

The shape of the driver elements 8 is not limited to the shape of acircular pole. It may be the shape of a sphere or a square pole. Thedriver elements preferably have a spherical shape because in this casethe driver elements and the piezoelectric element P1 are fixedly inpoint contact with each other.

The electrical connection members are not limited to the flexiblecables. For example, wires, contact pins, conductive rubbers, etc., maybe used. The above-described connection with the anisotropic conductiveadhesive sheet may be replaced by a different electrical connectionmethod, for example, connection with a low-melting metal, such assoldering, connection by wire bonding, connection with a non-anisotropicconductive adhesive sheet, connection with a conductive adhesive, suchas a liquid adhesive, connection by pressing, etc. The conductiverubbers may have a layered structure which includes a supporting layermade of, for example, silicone rubber as a principal constituent, and aconductive layer containing silicone rubber and metal particles ofsilver, or the like, and may be anisotropic so that it is nonconductingin the stacking direction. One of the short-side surfaces of thepiezoelectric element may be provided with one piece of the conductiverubber or may be provided with two pieces of the conductive rubber. Inthe case of using the conductive rubber, the conductive rubber may beused as the supporting portions 13 a and 13 c. In the case where one ofthe short-side surfaces of the piezoelectric element is provided withone piece of the conductive rubber, the non-conductive property of theconductive rubber in the stacking direction is utilized to provideinsulation of the power supply external electrodes 4 and the counterexternal electrodes 5, specifically insulation between the first powersupply external electrode 4A and the second power supply externalelectrode 4B, and insulation between a first counter external electrode5A and a second counter external electrode 5B. In this case, therespective conductive layers function as any of the first power supplyconductive member 6A, the second power supply conductive member 6B, thefirst counter conductive member 7A, and the second counter conductivemember 7B.

The first connection electrode J1 and the second connection electrode J2are provided at the longitudinal center of the principal surface of thepiezoelectric layer 1 and have a shape elongated in a directiongenerally perpendicular to the short sides of the principal surface ofthe piezoelectric layer 1. More preferably, as for the dimensions in thedirection of the long sides of the piezoelectric layer 1, the width ofthe first connection electrode J1 and the second connection electrode J2is preferably about 5% to 40% of the length of the long sides of thepiezoelectric layer 1. This is because, although a greater stretchingvibration occurs as the electrode areas of the first connectionelectrode J1 and the second connection electrode J2 increase, the secondmode bending vibration would be interrupted if the electrode areas areexcessively large. On the other hand, as for the dimensions in thedirection of the short sides of the piezoelectric layer 1, the firstconnection electrode J1 and the second connection electrode J2 shouldideally be provided over the entire short sides. However, if the firstconnection electrode J1 and the second connection electrode J2 reach theedges of the piezoelectric layer 1 at its lateral ends, it is difficultto provide insulation between the internal electrode layers. As such,the first connection electrode J1 and the second connection electrode J2are preferably provided over the principal surface of the piezoelectriclayer 1 except for the edges of the principal surface at its lateralends. Specifically, the first connection electrode J1 and the secondconnection electrode J2 are desirably provided over the entire principalsurface of the piezoelectric layer 1 except for a region extending fromthe respective edges of the principal surface of the piezoelectric layer1 at its lateral ends toward the lateral center by the distance equal tothe thickness of the piezoelectric layer 1. This applies to the thirdconnection electrode J3 and the fourth connection electrode J4 ofembodiment 5.

The number of power supply electrodes 2 of the first pattern and thenumber of power supply electrodes 2 of the second pattern are preferablyequal although they may not be equal. The power supply electrodes 2 ofthe first pattern and the power supply electrodes 2 of the secondpattern are preferably alternately provided although they may not bealternately provided. In embodiment 5, the number of counter electrodes3 of the third pattern and the number of counter electrodes 3 of thefourth pattern are preferably equal although they may not be equal. Thecounter electrodes 3 of the third pattern and the counter electrodes 3of the fourth pattern are preferably alternately provided although theymay not be alternately provided. This alternate arrangement improves thesymmetry of vibration of the piezoelectric element. Also, the alternatearrangement prevents generation of excessive vibration in thepiezoelectric element so that the energy loss can be greatly reduced.

The power supply electrodes 2 and counter electrodes 3 are preferablyconfigured so as not to be exposed on the principal surface of thepiezoelectric element although they may be exposed thereon. When thepower supply electrodes 2 and counter electrodes 3 are not exposed onthe principal surface of the piezoelectric element which has a largerarea among the external surfaces of the piezoelectric element, theprobability of occurrence of short circuits with peripheral metal partsdecreases.

The region where the power supply electrodes 2 and the counterelectrodes 3 are not overlapping when seen in the stacking direction ismore preferably a region extending from the respective edges of thepiezoelectric layer 1 at its longitudinal ends toward the longitudinalcenter by the distance equal to or greater than 10% of the longitudinaldimension of the piezoelectric layer 1. The region where the powersupply electrodes 2 and the counter electrodes 3 are not overlappingwhen seen in the stacking direction is preferably a region extendingfrom the respective edges of the piezoelectric layer 1 at itslongitudinal ends toward the longitudinal center by the distance equalto or greater than 20% of the longitudinal dimension of thepiezoelectric layer 1. In this case, near the edges of the piezoelectriclayer 1 at its longitudinal ends, only a small stress is created underthe first mode stretching vibration. Also, the connection between theshort-side surfaces of the piezoelectric element and the electricalconnection members can be less affected.

In the above-described embodiments, the movable element 9 which isdriven by applying a driving force from the ultrasonic actuator is inthe shape of a flat plate, to which the present invention is notlimited. Any structure may be adopted as the structure of the movableelement 9. For example, as shown in FIG. 21, the movable element may bea circular disk 9 which is rotatable around a predetermined axis X, withthe driver elements 8 of the ultrasonic actuator abutting thecircumferential surface 9 a of the circular disk 9. In the case of thisstructure, when the ultrasonic actuator is driven, the driver elements 8make a generally-elliptic movement, and accordingly, the circular disk 9is rotated around the predetermined axis X. Part of the mechanismincluding the piezoelectric element may be stationary or may be movable.

In the above-described embodiments, the supporting body is formed by thecase 11 but may be formed by any structure.

The voltage applied to the second power supply electrode 2B is differentin phase from the reference voltage applied to the first power supplyelectrode 2A by generally +90 degrees or by generally −90 degrees, towhich however the present invention is not limited. A voltage of adifferent phase difference from the reference voltage may be applied.Also, the voltage may be applied to only one of the first power supplyelectrode 2A and the second power supply electrode 2B.

In the above-described embodiments, the ultrasonic actuator is supportedusing the supporting portions 13 a, 13 b and 13 c. However, the presentinvention is not limited to this example. For example, as shown in FIG.22, only the supporting portion 13 b is provided on one of the twolong-side surfaces of the piezoelectric element on which the driverelements are not provided. This supporting portion 13 b restricts themovement of the piezoelectric element in the driving direction (thelong-side direction of the principal surface) and allows the movement ofthe driver elements in a direction in which the driver elements abut themovable element 9 (the short-side direction of the principal surface).The supporting portion 13 b generates a pressing force in a direction inwhich the driver elements abut the movable element and increases thefrictional force between the driver elements and the movable element.

The present invention is not limited to the above-described embodimentsand can be implemented in various other forms without departing from thespirit of the invention. The embodiments are merely exemplary in allaspects and should not be construed as limiting. The scope of theinvention is defined only by claims and is not restricted by thespecification. Variations and modifications equivalent to the claimedinventions are all within the scope of the present invention.

Industrial Applicability

The present invention is applicable to a highly-reliable ultrasonicactuator, for example, a driving force generator which is for use in avariety of electronic devices and other types of devices.

1. An ultrasonic actuator, comprising: a piezoelectric element; and aflexible cable electrically connected to the piezoelectric element,wherein the piezoelectric element includes a plurality of generallyrectangular piezoelectric layers, a power supply electrode provided on aprincipal surface of at least one of the plurality of piezoelectriclayers, a counter electrode provided to face the power supply electrodewith the piezoelectric layer interposed therebetween, a power supplyexternal electrode provided on one of external surfaces of thepiezoelectric element which is perpendicular to the principal surface ofthe piezoelectric layer, and which is parallel to short sides of theprincipal surface, the power supply external electrode beingelectrically coupled to the power supply electrode, and a counterexternal electrode provided on one of the external surfaces of thepiezoelectric element which is perpendicular to the principal surface ofthe piezoelectric layer, and which is parallel to the short sides of theprincipal surface, the counter external electrode being electricallycoupled to the counter electrode, the flexible cable includes a powersupply conductive member electrically connected to the power supplyexternal electrode, and a counter conductive member electricallyconnected to the counter external electrode, the power supply externalelectrode includes a first power supply external electrode supplied witha first driving voltage, and a second power supply external electrodesupplied with a second driving voltage which is different in phase fromthe first driving voltage, the power supply electrode includes a firstpower supply electrode provided on the principal surface of the at leastone of the plurality of piezoelectric layers, the first power supplyelectrode being electrically coupled to the first power supplyelectrode, and a second power supply electrode provided on the principalsurface which has the first power supply electrode thereon or on aprincipal surface of another one of the piezoelectric layers which isdifferent from the principal surface that has the first power supplyelectrode thereon, the second power supply electrode being notelectrically coupled to the first power supply electrode and beingelectrically coupled to the second power supply electrode, the powersupply conductive member includes a first power supply conductive memberelectrically connected to the first power supply external electrode, asecond power supply conductive member electrically connected to thesecond power supply external electrode, wherein one of two externalsurfaces of the piezoelectric element which are perpendicular to theprincipal surface of the piezoelectric layer, and which are parallel tothe short sides of the principal surface includes the first power supplyexternal electrode, and does not include the second power supplyexternal electrode, and the other one of the two external surfacesincludes the second power supply external electrode, and does notinclude the first power supply external electrode.
 2. The ultrasonicactuator of claim 1, wherein the first power supply electrode isprovided in two of four divisional regions of the principal surface ofthe piezoelectric layer which are defined by halving the principalsurface with respect to its longitudinal and lateral directions, the twodivisional regions being aligned in a first diagonal direction of theprincipal surface of the piezoelectric layer, and the second powersupply electrode is provided in two of the four divisional regions ofthe principal surface of the piezoelectric layer which are defined byhalving the principal surface with respect to its longitudinal andlateral directions, the two divisional regions being aligned in a seconddiagonal direction of the principal surface of the piezoelectric layer.3. The ultrasonic actuator of claim 2, wherein the power supplyelectrode includes a first connection electrode which is provided on theprincipal surface of the piezoelectric layer that has the first powersupply electrode thereon, and which electrically connects the firstpower supply electrodes provided in the two of the four divisionalregions aligned in the first diagonal direction, and a second connectionelectrode which is provided on the principal surface of thepiezoelectric layer that has the second power supply electrode thereonand that is different from the piezoelectric layer having the firstpower supply electrode thereon, and which electrically connects thesecond power supply electrodes provided in the two of the fourdivisional regions aligned in the second diagonal direction.
 4. Theultrasonic actuator of any of claim 3, wherein the first connectionelectrode and the second connection electrode are provided at alongitudinal center of the principal surface of the piezoelectric layer,and have a shape elongated in a direction generally parallel to theshort sides of the principal surface of the piezoelectric layer.
 5. Theultrasonic actuator of claim 1, wherein an area of the power supplyelectrode and an area of the counter electrode are not overlapping nearthe short sides of the principal surface of the piezoelectric layer whenseen in a direction perpendicular to the principal surface of thepiezoelectric layer.
 6. The ultrasonic actuator of claim 1, wherein theflexible cable includes a first flexible cable electrically connected tothe piezoelectric element at one of two external surfaces of thepiezoelectric element which are perpendicular to the principal surfaceof the piezoelectric layer, and which are parallel to the short sides ofthe principal surface, and a second flexible cable electricallyconnected to the piezoelectric element at the other one of the twoexternal surfaces, the first flexible cable has a shape symmetricalabout a plane which passes through midpoints of the short sides of theprincipal surface of the piezoelectric layer, and which is perpendicularto the one of the two external surfaces, and the second flexible cablehas a shape symmetrical about a plane which passes through the midpointsof the short sides of the principal surface of the piezoelectric layer,and which is perpendicular to the other one of the two externalsurfaces.
 7. The ultrasonic actuator of claim 6, wherein the firstflexible cable and the second flexible cable have a shape symmetricalabout a plane which passes through midpoints of long sides of theprincipal surface of the piezoelectric layer, and which is perpendicularto the principal surface.
 8. The ultrasonic actuator of claim 1, whereinthe flexible cable includes a first flexible cable electricallyconnected to the piezoelectric element at one of two external surfacesof the piezoelectric element which are perpendicular to the principalsurface of the piezoelectric layer, and which are parallel to the shortsides of the principal surface, and a second flexible cable electricallyconnected to the piezoelectric element at the other one of the twoexternal surfaces, and the first flexible cable and the second flexiblecable have a shape symmetrical about a plane which passes throughmidpoints of long sides of the principal surface of the piezoelectriclayer, and which is perpendicular to the principal surface.
 9. Theultrasonic actuator of claim 1, further comprising: a driver elementprovided on one of external surfaces of the piezoelectric element whichis perpendicular to the principal surface of the piezoelectric layer,and which is parallel to long sides of the principal surface.
 10. Theultrasonic actuator of claim 1, wherein a resonance frequency of avibration in a long-side direction of the principal surface of thepiezoelectric layer is substantially equal to a resonance frequency of avibration in a short-side direction of the principal surface.
 11. Theultrasonic actuator of claim 1, wherein the piezoelectric element isconfigured to cause a resonant vibration in a long-side direction of theprincipal surface of the piezoelectric layer, and a resonant vibrationin a short-side direction of the principal surface upon application ofan alternating voltage at a predetermined frequency between the powersupply electrode and the counter electrode.